1.Engineering Research Center of Internet of Things Technology Applications (Ministry of Education), Department of Electronic Engineering, Jiangnan University, Wuxi 214122, China 2.Beijing Smart-Chip Microelectronics Technology Co., Ltd., Beijing Engineering Research Center of High-reliability IC with Power Industrial Grade, Beijing 102200, China 3.State Key Discipline Laboratory of Wide Band-gap Semiconductor Techonology, Xidian University, Xi’an 710071, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 61504050, 11604124, 51607022) and the Laboratory Open Fund of Beijing Smart-chip Microelectronics Technology Co., Ltd, China
Received Date:04 September 2020
Accepted Date:01 December 2020
Available Online:01 April 2021
Published Online:20 April 2021
Abstract:In this work, we first measure the forward temperature-dependent current-voltage (T-I-V) characteristics of the GaN-based Schottky diodes grown on the bulk GaN substrates, and then study the transport mechanisms of the forward current and the low-frequency current noise behaviors under various injection levels. The results are obtained below. 1) In a forward high-bias region the thermionic emission current dominates, and the extracted barrier height is about 1.25 eV at T = 300 K, which is close to the value measured by capacitance-voltage sweeping. 2) In a forward low-bias region (V < 0.8 V) the current is governed by the trap assist tunneling process, having an ideality factor much larger than 1, and the derived barrier height is about 0.92 eV at T = 300 K, which indicates that the conductive dislocation should be mainly responsible for the excessive leakage current, having a reduced barrier around the core of dislocations. 3) The Lorentzian noise appears only at very small current (I < 1 μA) and low frequency (f < 10 Hz), whose typical time constant is extracted to be about 30 ms, depending on the multiple capture and release process of electrons via defects. 4) At a higher frequency and current, the low-frequency 1/f noise becomes important and the corresponding coefficient is determined to be about 1.1, where the transport is affected by the random fluctuation of the Schottky barrier height. Keywords:GaN Schottky diode/ transport mechanism/ low-frequency noise
图 2 Ni/Au/n-GaN肖特基二极管的掺杂浓度与结深关系曲线, 内插图为高频$ 1/C^2 $-V数据图 Figure2. Dopant concentration as a function of junction depth of the fabricated Ni/Au/n-GaN Schottky diode. The inset shows a plot of $ 1/C^2 $vs. V.
3.结果与讨论与p-n结不同, 肖特基接触的正向电流的载流子为多子. 图3所示为n型半导体肖特基结构在正向偏压下的三种基本电流输运过程. 图中, EFm, EFn分别是金属和半导体的费米能级, Ec为半导体的导带, $q{\phi _{\rm Bn}}$是金属的功函数, $q{\phi _n}$为Ec和费米能级之间的能量差. 从图3可以看出: 1)温度较高时, 高能电子从半导体越过势垒进入金属的经典热发射(TE)机制; 2)温度较低时, 低能电子从电场获得能量, 从半导体隧穿至金属的场发射(FE)机制; 3)中等温度时(例如300 K), 以可比较的TE和FE分量为主的热场发射(TFE)机制. 图 3 正向偏压下的三种输运机制: 1, TE; 2, TFE; 3, FE, 实点代表GaN中的自由电子 Figure3. Three basic transport processes under forward bias: 1 is thermionic emission, 2 is thermal field emission, 3 is field emission. The solid dots represent electrons in GaN, and the solid ponts are free electron in GaN.
图4所示为Ni/Au/n-GaN肖特基二极管的T-I-V特性曲线, 测试温度范围为300—450 K. 可以看出, 在正向低偏压下(V < 0.8 V), 电流随电压呈指数增长, 其斜率随温度升高逐渐减小; 而在高偏压下, 电流随着偏压增大逐渐向下弯曲, 此时串联电阻效应显著. 通常, 理想肖特基接触的电流行为可由经典TE理论来描述[11] 图 4 Ni/Au-GaN肖特基二极管的典型变温I-V特性曲线, 红色实线为300 K下TE模型 Figure4. Forward bias I-V characteristics of Ni/Au/n-GaN Schottky diode measured at different temperatures. The red solid line is the fitting line based on TE model at 300 K.
图 1 Ni/Au/n-GaN肖特基二极管的横截面结构示意图(a)和器件俯视图(b)
图 2 Ni/Au/n-GaN肖特基二极管的掺杂浓度与结深关系曲线, 内插图为高频
图 3 正向偏压下的三种输运机制: 1, TE; 2, TFE; 3, FE, 实点代表GaN中的自由电子
图 4 Ni/Au-GaN肖特基二极管的典型变温I-V特性曲线, 红色实线为300 K下TE模型
图 5 q?Bn和T的关系
图 6 (a) n, (b) E0, (c) 
图 7 GaN可导位错的能带结构示意图
图 8 I = 1 nA到100 μA的低频噪声谱