Browsing by Subject "Normally-off"
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Item Open Access Design, fabrication, and characterization of normally-off GaN HEMTS(2019-07) Gülseren, Melisa EkinGaN-based high-electron-mobility transistors (HEMTs) have been developing rapidly from the time when they were first demonstrated in the 1990s. They have consistently been presented as a displacement technology to silicon based power devices owing to the superior material properties of GaN such as high-electric breakdown field, high-electron saturation velocity, and high mobility. Normally-off GaN HEMT devices are particularly significant in power electronics applications. In this thesis, a comprehensive study of normally-off high-electron-mobility transistors is presented, including theoretical background review, theoretical analysis, physically-based device simulations, device fabrication and optimization and electrical characterization. p-GaN gate InAlN/GaN HEMT and recessed AlGaN/GaN MISHEMT devices have been successfully demonstrated.Item Open Access Investigation of a hybrid approach for normally-off GaN HEMTs using fluorine treatment and recess etch techniques(Institute of Electrical and Electronics Engineers Inc., 2019) Kurt, Gökhan; Gülseren, Melisa Ekin; Salkım, Gurur; Ural, Sertaç; Kayal, Ömer Ahmet; Öztürk, Mustafa; Bütün, Bayram; Kabak, M.; Özbay, EkmelA hybrid approach for obtaining normally off high electron mobility transistors (HEMTs) combining fluorine treatment, recess etch techniques, and AlGaN buffer was studied. The effects of process variations (recess etch depth and fluorine treatment duration) and epitaxial differences (AlGaN and carbon doped GaN buffers) on the DC characteristics of the normally off HEMTs were investigated. Two different epitaxial structures and three different process variations were compared. Epitaxial structures prepared with an AlGaN buffer showed a higher threshold voltage (V th = +3.59 V) than those prepared with a GaN buffer (V th = +1.85 V).Item Open Access Normally-off AlGaN/GaN MIS-HEMT with low gate leakage current using a hydrofluoric acid pre-treatment(Elsevier, 2019) Kurt, Gökhan; Gülseren, Melisa Ekin; Ghobadi, Türkan Gamze Ulusoy; Ural, Sertaç; Kayal, Ömer Ahmet; Öztürk, Mustafa; Bütün, Bayram; Kabak, Mehmet; Özbay, EkmelWe demonstrate the electrical performances of an AlGaN/GaN metal–insulator–semiconductor high electron mobility transistor (MIS-HEMT) with low gate leakage current (Ig). A low gate leakage current as low as the order of 10−11 A/mm was achieved from normally-off MIS-HEMT device (Vth = 2.16 V) with a partially recessed gate, fluorine treatment, and ALD Al2O3 gate dielectric layer. The gate leakage current decrease is attributed to the pre-treatment of the gate region with hydrofluoric acid (HF) and deionized water (DI) solution, which acts to remove the native oxide layer and thus decrease interface traps. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses demonstrate that the AlGaN surfaces are modified such that the surface roughness and native oxide introduced by the treatments used to achieve normally-off operation are remedied with the use of the pre-treatment.Item Open Access Selectively dry etched of p-GaN/InAlN heterostructures using BCI3-based plasma for normally-off HEMT technology(Institute of Physics Publishing Ltd., 2021-12-10) Toprak, Ahmet; Yılmaz, Doğan; Özbay, EkmelIn this paper, an alternative selective dry etching of p-GaN over InAlN was studied as a function of the ICP source powers, RF chuck powers and process pressures by using inductively coupled plasma reactive ion etching (ICP RIE) system. A recipe using only BCI3-based plasma with a resulting selectivity 13.5 for p-GaN in respect to InAlN was demonstrated. Surface roughness measurements depending on the etching time was performed by atomic force microscope (AFM) measurement and showed that a smooth etched surface with the root-mean-square roughness of 0.45 nm for p-GaN and 0.37 nm for InAlN were achieved. Normally-off p-GaN/InAlN HEMT devices were fabricated and tested by using the BCI3-based plasma we developed.