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Effect of reactor pressure on the growth rate and structural properties of GaN films

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Chinese Science Bulletin 2009年第15期54卷 2595-2598页

作者： ni jinyu hao yue zhang jincheng YANG LinAn Key Laboratory of Wide Band-Gap Semiconductor Materials and Devices School of Microelectronics Xidian University Xi'an710071 China

The effect of reactor pressure on the growth rate, surface morphology and crystalline quality of GaN films grown on sapphire by metalorganic chemical vapor deposition is studied. The results show that as the reactor pressure increases from 2500 to 20000 Pa, the GaN surface becomes rough and the growth rate of GaN films decreases. The rough surface morphology is associated with the initial high temperature GaN islands, which are large with low density due to low adatom surface diffusion under high reactor pressure. These islands prolong the occurrence of 2D growth mode and decrease the growth rate of GaN film. Meanwhile, the large GaN islands with low density lead to the reduction of threading dislocation density during subsequent island growth and coalescence, and consequently decrease the full width at half maximum of X-ray rocking curve of the GaN film.

关键词： GaN薄膜增长速度压力上升反应器结构特性金属有机物化学气相沉积表面形貌原子表面扩散

Development and characteristic analysis of enhancement-mode recessed-gate AlGaN/GaN HEMT

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Science China(Technological Sciences) 2008年第6期51卷 784-789页

作者： hao yue WANG Chong ni jinyu FENG Qian zhang jincheng MAO Wei Institute of Microelectronics Xidian Universityand Key Lab of Wide Band Gap Semiconductor Materials and DevicesXi’an 710071China

Fabrication of enhancement-mode high electron mobility transistors on AlGaN/GaN heterostructures grown on sapphire substrates is reported. These devices with 1 μm gate-length, 10 nm recessed-gate depth, 4 μm distance of source and drain exhibit a maximum drain current of 233 mA/mm at 1.5 V, a maximum transconductance of 210 mS/mm, and a threshold voltage of 0.12 V. The threshold voltage of these devices increased to 0.53 V after 500°C 5 min annealing in N2 ambient. The saturation drain current and transconductance of 15 nm recessed-gate depth reduced compared to those of 10 nm recessed-gate depth, but the threshold voltage increased to 0.47 V. The relations between threshold voltage, controlling ability of gate and recess depth were validated by testing C-V structures on AlGaN/GaN heterostructures with different etching depth.

关键词： enhacement-mode high electron mobility transistors AlGaN/GaN recessed-gate threshold voltage

Improved electrical properties of the two-dimensional electron gas in AlGaN/GaN heterostructures using high temperature AlN interlayers

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Science China(Technological Sciences) 2010年第6期53卷 1567-1571页

作者： XUE JunShuai,hao yue,zhang jincheng & ni jinyu Key Laboratory of Wide Band-Gap Semiconductors and Devices,School of Microelectronics,Xidian University,Xi’an 710071,China 1. Key Laboratory of Wide Band-Gap Semiconductors and Devices School of Microelectronics Xidian University Xi’an 710071 China

The electrical properties of two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures using high temperature (HT) AlN interlayers (ITs) grown on c-plane sapphire substrate by metal organic chemical vapor deposition (MOCVD) have been *** is found that the electrical properties (electron mobility and sheet carrier density) are improved compared with those in the conventional AlGaN/GaN heterostructures without HT AlN ITs,and the improved 2DEG properties result in the reduction of the sheet *** results from high resolution X-ray diffraction (HRXRD) and Raman spectroscopy measurements show that HT AlN ITs increase the in-plane compressive strain in the upper GaN layer,which enhances the piezoelectric polarization in it and consequently causes increasing of 2DEG density at the AlGaN/GaN ***,the compressive strain induced by HT AlN ITs leads to a less tensile strain in AlGaN barrier layer and causes positive and negative effects on the sheet carrier density of 2DEG,which counteract each *** HT AlN ITs reduce the lattice mismatch between the GaN and AlGaN layers and smooth the interface between them,thus increasing the electric mobility of 2DEG by weakening the alloy-related interface roughness and *** addition,the surface morphology of AlGaN/GaN heterostructures is improved by the insertion of HT AlN *** reason for the improved properties is discussed in this paper.

关键词： AlGaN/GaN heterostructures electrical properties two dimensional electron gas

Study of GaN MOS-HEMT using ultrathin Al_2O_3 dielectric grown by atomic layer deposition

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Science China(Technological Sciences) 2009年第9期52卷 2762-2766页

作者： yue YuanZheng,hao yue,FENG Qian,zhang jincheng,MA XiaoHua & ni jinyu Key Laboratory of Wide Band-Gap Semiconductor Materials and Devices,Xidian University,Xi’an 710071,China Key Laboratory of Wide Band-Gap Semiconductor Materials and Devices Xidian University Xi’an 710071 China

We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic-layer deposited (ALD) Al2O3 as the gate dielectric. Through further decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process,a device with maximum transconductance of 150 mS/mm was produced. The drain current of this 0.8 μm gate-length MOS-HEMT could reach 800 mA/mm at +3.0 V gate bias. Compared to a conventional AlGaN/GaN HEMT of similar design,better interface property,lower leakage current,and smaller capacitance-voltage (C-V) hysteresis were obtained,and the superiority of this MOS-HEMT device structure with ALD Al2O3 gate dielectric was exhibited.

关键词： ALD ultrathin Al2O3 AlGaN/GaN MOS-HEMT

Observation of Dislocation Etch Pits in GaN Epilayers by Atomic Force Microscopy and Scanning Electron Microscopy

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Journal of Semiconductors 2007年第4期28卷 473-479页

作者：高志远郝跃张进城张金凤陈海峰倪金玉西安电子科技大学微电子研究所西安710071

A combination of atomic force microscopy （AFM） and scanning electron microscopy （SEM） is used to characterize dislocation etch pits in Si-doped GaN epilayer etched by molten KOH. Three types of etch pits with different shapes and specific positions in the surface have been observed,and a model of the etching mechanism is proposed to explain their origins. The pure screw dislocation is easily etched along the steps that the dislocation terminates. Consequently a small Ga-polar plane is formed to prevent further vertical etching,resulting in an etch pit shaped like an inverted truncated hexagonal pyramid at the terminal chiasma of two surface steps. However, the pure edge dislocation is easily etched along the dislocation line,inducing an etch pit of inverted hexagonal pyramid aligned with the surface step. The polarity is found to play an important role in the etching process of GaN.

关键词： KOH etching dislocation GaN polarity

GaN MOS-HEMT Using Ultrathin Al_2O_3 Dielectric with f_(max) of 30.8GHz

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Journal of Semiconductors 2007年第11期28卷 1674-1678页

作者：郝跃岳远征冯倩张进城马晓华倪金玉西安电子科技大学宽禁带半导体材料与器件教育部重点实验室西安710071

We report on a GaN metal-oxide-semiconductor high electron mobility transistor （MOS-HEMT） using atomic-layer deposited （ALD） A1203 as the gate dielectric. Through decreasing the thickness of the gate oxide to 3.5nm,a device with maximum transconductance of 130mS/mm is produced. The drain current of this 1/~m gate- length MOS-HEMT can reach 720mA/mm at ＋ 3.0V gate bias. The unity current gain cutoff frequency and maxi- mum frequency of oscillation are obtained as 10.1 and 30.8GHz,respectively.

关键词： A1GaN/GaN MOS-HEMT ultrathin A1203