Browsing by Subject "Photodetector"

Now showing 1 - 20 of 30

Open Access
100-GHz resonant cavity enhanced Schottky photodiodes
(Institute of Electrical and Electronics Engineers, 1998) Onat, B. M.; Gökkavas, M.; Özbay, Ekmel; Ata, E. P.; Towe, E.; Ünlü, M. S.
Resonant cavity enhanced (RCE) photodiodes are promising candidates for applications in optical communications and interconnects where ultrafast high-efficiency detection is desirable. We have designed and fabricated RCE Schottky photodiodes in the (Al, In) GaAs material system for 900-nm wavelength. The observed temporal response with 10-ps pulsewidth was limited by the measurement setup and a conservative estimation of the bandwidth corresponds to more than 100 GHz. A direct comparison of RCE versus conventional detector performance was performed by high speed measurements under optical excitation at resonant wavelength (895 nm) and at 840 nm where the device functions as a single-pass conventional photodiode. A more than two-fold bandwidth enhancement with the RCE detection scheme was demonstrated.
Open Access
A1GaN UV photodetectors : from micro to nano
(2011) Bütün, Serkan
The absorption edge of AlGaN based alloys can be tuned from deep UV to near UV by changing the composition. This enables the use of the material in various technological applications such as military, environmental monitoring and biological imaging. In this thesis, we proposed and demonstrated various UV photodetectors for different purposes. The multi-band photodetectors have the unique ability to sense the UV spectrum in different portions at the same time. We demonstrated monolithically integrated dual and four-band photodetectors with multi layer structures grown on sapphire. This was achieved through epitaxial growth of multi AlGaN layers with decreasing Al content. We suggested two different device architectures. First one has separate filter and active layers, whereas the second one has all active layers which are used as filter layers as well. The full width at half maximum (FWHM) values for the dual band photodetector was 11 and 22 nm with more than three orders of magnitude inter-band rejection ratio. The self-filtering four band photodetector has FWHMs of 18, 17, 22 and 9 nm from longer to shorter bands. Whereas photodetector with separate filter layers has FWHMs of 8, 12, 11 and 8 nm, from longer to shorter bands. The overall inter-band rejection ration was increased from about one to two of magnitude after incorporating the passive filter layers. The plasmonic enhancement of photonic devices has attracted much attention for the past decade. However, there is not much research that has been conducted in UV region. In the second part of this thesis, we fabricated nanostructures on GaN based photodetectors and improved the responsivity of the device. We have fabricated Al nano-particles on sapphire with e-beam lithography. We characterized their response via spectral extinction measurements. We integrated these particles with GaN photodetectors and had enhancement of %50 at the plasmonic resonance of the nano-particles. Secondly, we have fabricated sub-wavelength photodetectors on GaN coupled with linear gratings. We had 8 fold enhancement in the responsivity at the plasmonic resonance frequency of the grating at normal incidence. Numerical simulations revealed that both surface plasmons and the unbound leaky surface waves played a role in the enhancement. We, finally, conducted basic research on the current transport mechanisms in Schottky barriers of AlGaN based materials. Experiments revealed that the tunneling current plays a major role in current transport. In addition incorporation, of a thin insulator between metalsemiconductor interface reduces the undesired surface states thereby improving the device performance.
Open Access
Adaptive metasurface designs for thermal camouflage, radiative cooling, and photodetector applications
(2022-01) Buhara, Ebru
Metamaterials, described as artificial sub-wavelength nanostructures, refer to a class of manufactured materials that possess distinctive electromagnetic features which cannot be found with natural materials. Thermal tunability, negative re-fractive index, perfect absorption, and invisible cloaking are examples of these attributes. Here, we design and implement metamaterials in four important ap-plication areas, namely 1) Multi-spectral infrared camouflage through excitation of plasmon-phonon polaritons in a visible-transparent hBN-ITO nanoantenna emitter, 2) Adaptive visible and short-wave infrared camouflage using a dynami-cally tunable metasurface, 3) Mid-infrared adaptive thermal camouflage using a phase-change material coupled dielectric nanoantenna, 4) An All-Dielectric Meta-surface Coupled with Two-Dimensional Semiconductors for Thermally Tunable Ultra-narrowband Light Absorption. In the first work, a metasurface design is developed to provide adaptive camou-flage in both visible and SWIR ranges. The proposed metasurface is made of an indium tin oxide (ITO) grating on a metal-insulator-metal (MIM, Ag-Sb2S3-Ag) nanocavity. In the amorphous state, the design operates as a colored transmis-sive window while, in the crystalline phase, it switches into a reflective mirror. In the meantime, the cavity acts as a thermally tunable host for the ITO nanoan-tenna providing tunable SWIR absorption to cover two transmissive regions at 1150-1350 nm (Region I) and 1400-1700 nm (Region II). It is found that the excitation of extended surface plasmons (ESPs) and guided mode resonances (GMRs) are responsible for light absorption in the SWIR range. Our theoretical calculations show that, besides the design’s ability for color adoption, the SWIR reflectance in Region I/Region II are reduced to 0.37/0.53 and 0.75/0.25 in the amorphous/crystalline phases. In the second work, a hybrid nanoantenna architecture made of ITO-hBN grating is proposed to satisfy all multi-spectral camouflage requirements. In this design, simultaneous excitation of plasmon-phonon polaritons in ITO and hBN leads to broadband absorption in the NTIR range and reflection in MWIR and LWIR ranges. Moreover, the bulk absorption in ITO film provides SWIR mode camouflage. Moreover, to highlight the importance of this hybrid design, the ITO-hBN design is compared with ITO-TiO2 heterostructure(TiO2 is a lossless dielectric in our desired ranges). Finally, the camouflage performance of the meta-surface is evaluated as the outgoing emission suppression when the metasurface design is on top of the blackbody object. In the third work, a PCM-dielectric based metasurface nanoantenna emitter design is proposed to achieve low observability at the MIR region by tailoring the spectral emissivity of the design. The proposed thermal nanoantenna emitter is composed of a high index dielectric (silicon (Si) in our case) nanograting on top of a thick silver (Ag) mirror. An ultrathin VO2 interlayer is embedded within the grating to actively tune its absorption response. The design geometries are adopted to place the resonance wavelengths in the atmospheric absorption win-dows for thermal camouflage applications. Based on the position of the VO2 layer, the optical response of the design in the metal phase can be diversely tuned from a narrowband to a broadband thermal emitter. Therefore, upon increase in the surface temperature, the proposed metasurface based thermal nanoantenna emitter turns into a broadband emitter with a stronger radiative thermal emission while it compatibly releases its heat based on the camouflage technology require-ment. The proposed design has perfect matching with atmospheric absorption windows so that it can efficiently release its heat without being observed by ther-mal camera systems. The detectability of the structure by a possible IR sensor is calculated using power calculations over the selected spectra. In addition, due to the hysteresis behavior of VO2, the calculations are done separately for cooling and heating conditions. In the fourth and final work, a dielectric based metasurface platform is pro-posed to achieve ultra-narrowband light absorption within a monolayer thick TMDC layer. For this purpose, the metasurface design is optimized. Then, this design is coupled with mono and multilayer TMDCs to observe better absorption results. For this purpose, MoS2, and WS2 are chosen as the most commonly used TMDCs. The coupling of light into Mie resonances, supported by dielec-tric nanograting, provides narrowband absorption within the TMDC layer. To reach further enhancement, a cavity design is integrated into this dielectric-based metasurface. For the best optimized design, the absorptance efficiency reaches to 0.85 and FWHM stays as narrow as 3.1 nm. Finally, the thermal tunability char-acteristic of the design is shown, without use of any phase change material. This is achieved due to strong light confinement within the design. Due to this con-finement, any small change in the refractive index is seen by the resonant design. Thus, the resonance frequency shifts and thermal tunability is acquired. The thermal sensitivity of the above-mentioned optimized design reaches to 0.0096 nm/◦C.
Open Access
An all-dielectric metasurface coupled with two-dimensional semiconductors for thermally tunable ultra-narrowband light absorption
(Springer, 2020) Buhara, Ebru; Ghobadi, Amir; Özbay, Ekmel
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted tremendous attention over the past decades. Due to their unique features such as high mobility and direct bandgap, they are suitable candidate for the optoelectronic devices. However, due to their ultrathin thickness, their optical absorption is quite weak, and therefore, a trapping scheme for strong light- matter interaction is essential to overcome this deficiency. To accomplish strong light absorption, loss-less dielectric-based metasurfaces with ideally no parasitic absorption are excellent choices. Herein, we report an ultra-narrowband thermally tunable all-dielectric metasurface coupled absorber with TMD monolayer. In this proposed structure, high absorption with ultra-narrow full-width-at-half-maximum (FWHM) is achieved. Different design configurations are studied to find the most suitable structure. In the optimized design, an absorptance as high as 0.85 with a FWHM of 3.1 nm is achieved. This structure also shows thermal sensitivity of 0.0096 nm/°C, without the use of any phase change material component. This architecture can be used as a 2D and highly efficient tunable single-color photodetector. The proposed dielectric metasurface can be adopted for other types of 2D and ultrathin semiconductor-based optoelectronics.
Open Access
AlxGa1-xN based solar blind Schottky photodiodes
(2004) Tut, Turgut
Photodetectors are essential components of optoelectronic integrated circuits and fiber optic communication systems. AlxGa1−xN is a promising material for optoelectronics and electronics. Applications include blue and green LEDs, blue laser diodes, high power-high frequency electronics, and UV photodetectors. Photodetectors that operate only in the λ < 280 nm spectrum are called solarblind detectors due to their blindness to solar radiation within the atmosphere. In this thesis, we present our efforts for the design, fabrication and characterization of Al0.38Ga62N/GaN based solar blind Schottky photodiodes. We obtained very low dark current, high quantum efficiency, high detectivity performance. Under 25 V reverse bias, we measured a maximum quantum efficiency of 71 percent at 254 nm and a maximum responsivity of 0.15 A/W at 253 nm for a 150 micron diameter device. To our knowledge, these are the best values reported in the literature. For a 30 micron device, 50 ps FWHM pulse response is observed. When the scope response is deconvoluted, a maximum 3-dB bandwidth of 4.0 GHz is obtained for 30 micron diameter Schottky photodiodes.
Open Access
A Comparative Passivation Study for InAs / GaSb Pin Superlattice Photodetectors
(IEEE Institute of Electrical and Electronics Engineers, 2013-08) Salihoglu, O.; Muti, A.; Aydınlı, Atilla
In the quest to find ever better passivation techniques for infrared photodetectors, we explore several passivation layers using atomic layer deposition (ALD). We compare the impact of these layers on detectors fabricated under same conditions. We use ALD deposited Al2O3, HfO2, TiO2, ZnO, plasma enhanced chemical vapor deposition deposited SiO2, Si3N4, and sulfur containing octadecanethiol self assembled monolayer passivation layers on InAs/GaSb p-i-n superlattice diodes with an average cutoff wavelength of 5.1 mu m. Passivated and unpassivated photodetectors compared for their electrical performances.
Open Access
Design, fabrication and characterization of high performance resonant cavity enhanced photodetectors
(1998) Bıyıklı, Necmi
Photodetectors are essential components of optoelectronic integrated circuits and fiber optic communication systems. For higher system performances, photoreceivers with high bandwidth-efficiency products are needed. A new family of photodetectors introduced in the early 90's offers high performance detection along with wavelength selectivity: resonant cavity enhanced (RCE) photodetectors. In this thesis, we present our efforts for the design, fabrication and characterization of AlGaAs/GaAs-based Schottky and p-i-n type RCE photodiodes operating within the first optical communication window. Epitaxial wafers are designed using scattering matrix method based simulations and grown with molecular beam epitaxy. Schottky photodiode was primarily designed for high-speed operation, where as in p-i-n structure we aim to achieve near unity quantum efficiency. Measurement results show reasonable agreement our theoretical simulations. Fabricated Schottky and p-i-n RCE photodiode samples demonstrated high bandwidth-efficiency products, 36 and 46 GHz respectively. These results indicate the best performances for RCE Schottky and p-i-n photodiodes reported in scientific literature.
Open Access
Design, fabrication and characterization of high-performance solarblind AlGaN photodetectors
(SPIE, 2005) Özbay, Ekmel
Design, fabrication, and characterization of high-performance AlxGal-xN-based photodetectors for solar-blind applications are reported. AlxGal-xN heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal (MSM) photodiodes. The resulting solar-blind AlGaN detectors exhibited low dark current, high detectivity, and high bandwidth.
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Enhanced photoresponse of PVP:GaSe nanocomposite thin film based photodetectors
(Institute of Physics Publishing Ltd., 2022-02-21) Demirtaş, T.; Odacı, C.; Aydemir, Umut
Two-dimensional materials have become the focus of attention of researchers in recent years. The demand for two-dimensional materials is increasing day by day, especially with the inadequacy of graphene in optical applications. In this context, the optical and electrical characteristics of the PVP:GaSe thin film nanocomposites were investigated. The surface morphologies of the samples were characterized by SEM, the thin film thicknesses and refractive index parameters were measured by the Ellipsometer method, the structural characteristics were obtained by XRD, and Raman and PL spectroscopy was used to determine the optical characteristics. Critical parameters of Au/PVP:GaSe/n-Si photodetector were calculated under various illumination intensities. It is observed that photodetector with PVP:%5GaSe thin film has the best performance results. According to the experimental results, its responsivity, external quantum efficiency, and detectivity values are 0.485 A W−1, %86, and 1.14 × 107 cm Hz1/2 W−1 respectively.
Open Access
Fabrication and characterization of graphene/AlGaN/GaN ultraviolet Schottky photodetector
(Institute of Physics Publishing, 2016) Kumar, M.; Jeong, H.; Polat, K.; Okyay, Ali Kemal; Lee, D.
We report on the fabrication and characterization of a Schottky ultraviolet graphene/AlGaN/GaN photodetector (PD). The fabricated device clearly exhibits rectification behaviour, indicating that the Schottky barrier is formed between the AlGaN and the mechanically transferred graphene. The Schottky parameters are evaluated using an equivalent circuit with two diodes connected back-to-back in series. The PD shows a low dark current of 4.77 × 10-12 A at a bias voltage of -2.5 V. The room temperature current-voltage (I-V) measurements of the graphene/AlGaN/GaN Schottky PD exhibit a large photo-to-dark contrast ratio of more than four orders of magnitude. Furthermore, the device shows peak responsivity at a wavelength of 350 nm, corresponding to GaN band edge and a small hump at 300 nm associated to the AlGaN band edge. In addition, we examine the behaviour of Schottky PDs with responsivities of 0.56 and 0.079 A W-1 at 300 and 350 nm, respectively, at room temperature. © 2016 IOP Publishing Ltd.
Open Access
Fabrication and characterization of high speed resonant cavity enhanced Schottky photodiodes
(1996) Islam, M. Saiful
High speed, high external quantum efficiency and narrow spectral linewidth make resonant cavity enhanced (RC E) Schottky photodetector a good candidate for telecommunication applications. In this thesis, we present our work for the design, fabrication and characterization of a RCE Schottky photodiode with high quantum efficiency and high speed. We present experimental results on a RCE photodiode having an operating wavelength of 900 nm. The absorption takes place in a thin InGaAs layer placed inside the GaAs cavity. The active region was grown above a highreflectivity GaAs/AIAs quarter-wavelength Bragg reflector. The top mirror consisted of a 200A thin Au layer which also acted as Schottky metal of the device. An external quantum efficiency of 55% was obtained from our devices. We demonstrate that the spectral response can be tailored by etching the top surface of the microcavity. Our high speed measurements yielded a FW HM of 30 ps, which is the record response for any RCE Schottky photodiode ever reported.
Open Access
Gibbs free energy assisted passivation layers
(SPIE, 2016) Salihoğlu, Ömer; Tansel, T.; Hoştut, M.; Ergun, Y.; Aydınlı, Atilla
Reduction of surface leakage is a major challenge in most photodetectors that requires the elimination of surface oxides on etched mesas during passivation. Engineering the passivation requires close attention to chemical reactions that take place at the interface during the process. In particular, removal of surface oxides may be controlled via Gibbs reactivity. We have compared electrical performance of type-II superlattice photodetectors, designed for MWIR operation, passivated by different passivation techniques. We have used ALD deposited Al2O3, HfO2, TiO2, ZnO, PECVD deposited SiO2, Si3N4 and sulphur containing octadecanethiol (ODT) selfassembled monolayers (SAM) passivation layers on InAs/GaSb p-i-n superlattice photodetectors with cutoff wavelength at 5.1 μm. In this work, we have compared the result of different passivation techniques which are done under same conditions, same epitaxial structure and same fabrication processes. We have found that ALD deposited passivation is directly related to the Gibbs free energy of the passivation material. Gibbs free energies of the passivation layer can directly be compared with native surface oxides to check the effectiveness of the passivation layer before the experimental study.
Open Access
Graphene based flexible electrochromic devices
(Nature Publishing Group, 2014-10-01) Polat, E. O.; Balci, O.; Kocabas, C.
Graphene emerges as a viable material for optoelectronics because of its broad optical response and gate-tunable properties. For practical applications, however, single layer graphene has performance limits due to its small optical absorption defined by fundamental constants. Here, we demonstrated a new class of flexible electrochromic devices using multilayer graphene (MLG) which simultaneously offers all key requirements for practical applications; high-contrast optical modulation over a broad spectrum, good electrical conductivity and mechanical flexibility. Our method relies on electro-modulation of interband transition of MLG via intercalation of ions into the graphene layers. The electrical and optical characterizations reveal the key features of the intercalation process which yields broadband optical modulation up to 55 per cent in the visible and near-infrared. We illustrate the promises of the method by fabricating reflective/transmissive electrochromic devices and multi-pixel display devices. Simplicity of the device architecture and its compatibility with the roll-to-roll fabrication processes, would find wide range of applications including smart windows and display devices. We anticipate that this work provides a significant step in realization of graphene based optoelectronics.
Open Access
The growth, fabrication and characterization of high performance AI(formula)Ga(formula)N metal-semiconductor-metal photodiodes
(2006) Bütün, Serkan
High performance UV photodetectors have attracted unwarranted attention for various applications, such as in military, telecommunication, and biological imaging, as an AlxGa1-xN material system is also rather suitable for such applications. Its direct band gap covers the spectrum from 200 nm to 360 nm by way of changing the Al concentration in the compound. In this present thesis, the design and growth of an Al0.75Ga0.25N template on sapphire substrate and a deep-UV photodiode with a cut off wavelength of 229 nm that was fabricated on the Al0.75Ga0.25N template is presented. A responsivity of 0.53 A/W was attained corresponding to a detectivity of 1.64 × 1012 cmHz 1/2/W at a 50 V bias and 222 nm UV light illumination. The UV/VIS rejection ratio of seven orders of magnitude was achieved from the fabricated devices. The second work that was conducted in this thesis was the growth of a semiinsulating (SI-) GaN template. We also fabricated visible-blind photodetectors on this semi-insulating (SI-) GaN template. Furthermore, we fabricated identical samples on a regular GaN template in order to investigate any possible i improvement. The improvement found was obvious in terms of dark current. A dark current density of 1.96 × 10-10 A/cm2 at a 50 V bias voltage for an SI-GaN photodetector was obtained, which is four orders of magnitude lower than devices on a regular GaN template. Devices on an SI-GaN had very high detectivity, and therefore, SI-GaN was used for low level power detection. The photogenerated current was well above the dark current that was under the illumination of just a few picowatts of UV light.
Open Access
High speed and high efficiency infrared photodetectors
(2004) Kimukin, İbrahim
The increasing demand for telecommunication systems resulted in production of high performance components. Photodetectors are essential components of optoelectronic integrated circuits and fiber optic communication systems. We successfully used resonant cavity enhancement technique to improve InGaAs based p-i-n photodetectors. The detectors had 66% peak quantum efficiency at 1572 nm which showed 3 fold increases with respect to similar photodetector without resonant cavity. The detectors had 28 GHz 3-dB bandwidth at the same time. The bandwidth efficiency product for these detectors was 18.5 GHz, which is one of the best results for InGaAs based vertical photodetector. The interest in high speed photodetectors is not limited to fiber optic networks. In the recent years, data communication through the air has become popular due to ease of installation and flexibility of these systems. Although the current systems still operate at 840 nm or 1550 nm wavelengths, the advantage of mid-infrared wavelengths will result in the production of high speed lasers and photodetectors. InSb based p-i-n type photodetectors were fabricated and tested for the operation in the mid-infrared (3 to 5 µm) wavelength range. The epitaxial layers were grown on semi-insulating GaAs substrate by molecular beam epitaxy method. The detectors had low dark noise and high differential resistance around zero bias. Also the responsivity measurements showed 49% quantum efficiency. The detectivity was measured as 7.98×109 cm Hz1/2/W for 60 µm diameter detectors. Finally the high speed measurements showed 8.5 and 6.0 GHz bandwidth for 30 µm and 60 µm diameter detectors, respectively.
Open Access
High-performance AlxGA1-xN-Based UV photodetectors for visible/solar-blind applications
(2004) Bıyıklı, Necmi
High-performance detection of ultraviolet (UV) radiation is of great importance for a wide range of applications including flame sensing, environmental (ozone layer) monitoring, detection of biological/chemical agents, missile early warning systems, and secure intersatellite communication systems. These applications require high-performance UV photodetectors with low dark current, high responsivity, high detectivity, and fast time response. The widebandgap AlxGa1−xN ternary alloy is well-suited as a photodetector material for operation in the wavelength range of 200 nm to 365 nm. Its outstanding material properties (direct bandgap, tunable cut-off, allows heterostructures, intrinsically solar-blind) make AlxGa1−xN suitable for a variety of harsh environments. If properly constructed, AlxGa1−xN-based photodetectors could offer significant advantages over the older photomultiplier tube (PMT) technology in terms of size, cost, robustness, complexity, dark current, bandwidth, and solar-blind operation. The motivation behind this work is the need for high-performance, solid-state UV photodetectors that can be cost-effectively manufactured into high-density arrays. We have designed, fabricated, and characterized several visible/solar-blind AlxGa1−xN photodiode samples. With solar-blind AlxGa1−xN photodiode samples, we achieved excellent device performance in almost all aspects. Very low dark currents were measured with heterostructure AlxGa1−xN Schottky and p-i-n samples. The extremely low leakage characteristics resulted in record detectivity and noise performance. Detectivity performance comparable to PMT detectivity was achieved. True solar-blind operation (sub-280 nm cut-off) with high visible rejection was demonstrated. In addition, we improved the bandwidth performance of AlxGa1−xN-based solar-blind photodetectors by over an order of magnitude. Solar-blind Schottky, p-i-n, and metal-semiconductor-metal photodiode samples exhibited very fast pulse response with multi-GHz bandwidths.
Open Access
High-performance solar-blind AlGaN photodetectors
(SPIE, 2005) Özbay, Ekmel; Tut, Turgut; Bıyıklı, N.
Design, fabrication, and characterization of high-performance Al xGa1-xN-based photodetectors for solar-blind applications are reported. AlxGa1-xN heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3 fA leakage currents at 6 V and 12 V reverse bias were measured on p-i-n and Schottky photodiode samples respectively. The excellent current-voltage (I-V) characteristics led to a detectivity performance of 4.9×1014 cmHz1/2W-1. The MSM devices exhibited photoconductive gain, while Schottky and p-i-n samples displayed 0.15 A/W and 0.11 A/W peak responsivity values at 267 nm and 261 nm respectively. All samples displayed true solar-blind response with cut-off wavelengths smaller than 280 nm. A visible rejection of 4×104 was achieved with Schottky detector samples. High speed measurements at 267 nm resulted in fast pulse responses with >GHz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.
Open Access
High-performance solar-blind photodetectors based on AlxGa 1_xN heterostructures
(IEEE, 2004) Özbay, Ekmel; Bıyıklı, Necmi; Kimukin, I.; Kartaloglu, T.; Tut, T.; Aytür, O.
Design, fabrication, and characterization of high-performance AI xGa1-xN-based photodetectors for solar-blind applications are reported. AlxGa1-xN heterostructures were designed for Schottky. p-i-n, and metal-semicondnctor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3 fA, leakage currents at 6-V reverse bias were measured on p-i-n samples. The excellent current-voltage (I-V) characteristics led to a detectivity performance of 4.9×1014 cmHz1/2W -1. The MSM devices exhibited photoconductive gain, while Schottky and p-i-n samples displayed 0.09 and 0.11 A/W peak responsivity values at 267 and 261 nm, respectively. A visible rejection of 2×104 was achieved with Schottky samples. High-speed measurements at 267 nm resulted in fast pulse responses with greater than gigahertz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.
Open Access
High-speed GaAs-based resonant-cavity-enhanced 1.3-μm photodetector
(SPIE, 2000) Özbay, Ekmel; Kimukin, İbrahim; Bıyıklı, Necmi; Gary, T.
High-speed photodetectors operating at 1.3 and 1.55 μm are important for long distance fiber optic based telecommunication applications. We fabricated GaAs based photodetectors operating at 1.3 μm that depend on internal photoemission as the absorption mechanism. Detectors using internal photoemission have usually very low quantum efficiency. We increased the quantum efficiency using resonant cavity enhancement effect. Resonant cavity enhancement effect also introduced wavelength selectivity which is very important for wavelength division multiplexing based communication systems. The top-illuminated Schottky photodiodes were fabricated by a microwave-compatible monolithic microfabrication process. The top metal layer serves as the top mirror of the Fabry-Perot cavity. Bottom mirror is composed of 15 pair AlAs/GaAs distributed Bragg reflector. We have used transfer matrix method to simulate the optical properties of the photodiodes. Our room temperature quantum efficiency measurement and simulation of our photodiodes at zero bias show that, we have achieved 9 fold enhancement in the quantum efficiency, with respect to a similar photodetector without a cavity. We also investigated the effect of reverse bias on quantum efficiency. Our devices are RC time constant limited with a predicted 3-dB bandwidth of 70 GHz.
Open Access
High-Speed InSb photodetectors on GaAs for mid-IR applications
(IEEE, 2004) Kimukin, I.; Bıyıklı, Necmi; Kartaloǧlu, T.; Aytür, O.; Özbay, Ekmel
We report p-i-n type InSb-based high-speed photodetectors grown on GaAs substrate. Electrical and optical properties of photodetectors with active areas ranging from 7.06 × 10 -6 cm 2 to 2.25 × 10 -4 cm 2 measured at 77 K and room temperature. Detectors had high zero-bias differential resistances, and the differential resistance area product was 4.5 Ω cm 2. At 77 K, spectral measurements yielded high responsivity between 3 and 5 μm with the cutoff wavelength of 5.33 μm. The maximum responsivity tor 80-μm diameter detectors was 1.00 × 10 5 V/W at 435 μm while the detectivity was 3.41×10 9 cm Hz 1/2/W. High-speed measurements were done at room temperature. An optical parametric oscillator was used to generate picosecond full-width at half-maximum pulses at 2.5 μm with the pump at 780 mm. 30-μm diameter photodetectors yielded 3-dB bandwidth of 8.5 GHz at 2.5 V bias.