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GaN based Schottky barrier diode (SBD) possesses advantages including high power density, high conversion efficiency, and excellent switching characteristics. During heteroepitaxial growth of GaN, a high density of threading dislocations is inevitably introduced, which can degrade device reliability. This paper reports a low dislocation density N+/N– GaN quasi-vertical SBD fabricated on a freestanding GaN substrate. The characterization results of high-resolution X-ray diffraction and atomic force microscopy demonstrate that the high-quality epitaxial layer with a total dislocation density of 1.01 × 108 cm–2 and a root mean square surface roughness of 0.149 nm is achieved on a freestanding GaN substrate. The device prepared based on a high-quality epitaxial layer exhibits an ultra-low leakage current density of 10–5 A/cm2 at a reverse voltage of –5 V, without employing any edge termination structures or field plates or plasma treatment. Compared with the devices prepared on sapphire substrates using identical processes, the device prepared in this work reduces the reverse leakage current by four orders of magnitude. The experimental results show that the quasi-vertical GaN based SBD fabricated on a freestanding GaN substrate significantly reduces reverse leakage current and substantially enhances the overall electrical performance of the device. By employing emission-microscope (EMMI), leakage current in quasi-vertical SBD is identified to be primarily localized at the anode edge, and the underlying leakage mechanism is elucidated. Finally, temperature-dependent measurements demonstrate that the device maintains a leakage current below 10–3 A/cm2 at 100 ℃, confirming the potential of quasi-vertical SBD on freestanding GaN substrate for practical applications.
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Keywords:
- freestanding gallium nitride /
- dislocation density /
- quasi-vertical schottky diode /
- electrical properties
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图 1 准垂直GaN SBD器件的制备工艺流程图
Figure 1. Preparation process flow chart of quasi vertical GaN SBD device.
图 2 准垂直结构GaN SBD器件的SEM图
Figure 2. SEM image of GaN SBD device with quasi vertical structure.
图 3 样品a和样品b的(002)面(a)和(102)面(b)的XRD摇摆曲线图
Figure 3. XRD rocking curves of (002) plane (a) and (102) plane (b) of samples a and b.
图 4 样品a和样品b的AFM测试图
Figure 4. AFM images of sample a and sample b.
图 5 样品a和样品b室温下Raman图
Figure 5. Raman spectra of sample a and sample b at room temperature.
图 6 器件a和器件b在半对数坐标下的正反向I-V曲线
Figure 6. Forward and reverse I-V curves of device a and device b in semi-logarithmic coordinates.
图 7 器件a和器件b的击穿特性曲线
Figure 7. Breakdown characteristic curves of device a and device b.
图 8 半对数坐标下器件a(左)和器件b(右)正反向I-V特性随温度的变化关系
Figure 8. Forward and backward I-V characteristics of device a (left) and device b (right) with temperature in semi-logarithmic coordinates.
图 9 反向偏压10 V下器件a(左)和器件b(右)的EMMI图像
Figure 9. EMMI images of device a (left) and device b (right) under reverse bias of 10 V.
表 1 两组样品在(002)和(102)晶面的半高宽(FWHM)和位错密度
Table 1. FWHM and dislocation density of two groups of samples on the (002) and (102) crystal plane.
编号 (002)/
arcsec(102)/
arcsec螺位错密
度/cm–2刃位错密
度/cm–2总位错密
度/cm–2样品a 96 125 1.85×107 8.28×107 1.01×108 样品b 319 717 2.04×108 2.73×109 2.93×109 
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