Mechanisms of current collapse and gate leakage currents in AlGaN/GaN heterostructure field effect transistors
Mechanisms of current collapse and gate leakage currents in AlGaN/GaN heterostructure field effect transistors
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DOI：
10.1116/1.1589520
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发表时间：
2003-07-01
影响因子：
1.4
通讯作者：
Hashizume, T
中科院分区：
文献类型：
--
作者：
Hasegawa, H;Inagaki, T;Hashizume, T
为了阐明AlGaN/GaN异质结构场效应晶体管（HFET）中漏极电流崩溃和栅极漏电流的机制，使用无栅极HFET结构和AlGaN肖特基二极管结构分别研究了器件的非栅极部分和肖特基栅极部分的详细电特性。无栅极器件经过等离子体处理和表面钝化工艺，包括我们新型的基于 Al2O3 的表面钝化。由于表面态的虚拟选通，无栅极 HFET 的直流 I-V 曲线呈高度非线性。在漏极应力之后，暴露在空气中、经过 H-2 等离子体处理和 SiO2 沉积的无栅极 HFET 表现出最初的大幅度指数电流瞬变，随后出现较小、缓慢且高度非指数的响应。前者可以通过 E-c-0.37eV 的深层施主的发射来解释，后者可以通过表面态的发射来解释。还观察到具有应力依赖性捕获势垒的捕获瞬变。 X 射线光电子能谱 (XPS) 研究表明 0.37 eV 深的供体与 N 空位相关。另一方面，经 N-2 等离子体处理和 Al2O3 钝化的样品中没有发生电流瞬变。肖特基二极管的 I-V 曲线的温度依赖性极小，并且反向电流异常大。它们可以通过“薄表面势垒”（TSB）模型来解释，其中热电子场发射和通过深施主形成的 TSB 区域的场发射会产生漏电流路径。通过结合无栅极 HFET 和肖特基二极管的研究结果，提出了 AlGaN 自由表面和肖特基界面的新近表面电子态统一模型。它由 U 形表面态连续体和 N 空位相关的近表面离散深层施主组成。该模型可以统一解释 AlGaN/GaN HFET 中观察到的大栅极泄漏和漏极电流崩溃。研究还表明，我们的新型 Al2O3 钝化剂当也用作栅极绝缘体时，可以完全抑制电流崩塌和栅极泄漏。 (C) 2003 年美国真空协会。
In order to clarify the mechanisms of drain current collapse and gate leakage currents in the AlGaN/GaN heterostructure field effect transistor (HFET), detailed electrical properties of the ungated portion and Schottky-gated portion of the device were investigated separately, using a gateless HFET structure and an AlGaN Schottky diode structure. The gateless device was subjected to plasma treatments and surface passivation processes including our novel Al2O3-based surface passivation. dc I-V curves of gateless HFETs were highly nonlinear due to virtual gating by surface states. After drain stress, air-exposed, H-2 plasma-treated and SiO2-deposited gateless HFETs showed an initial large-amplitude exponential current transient followed by a subsequent smaller, slow, and highly nonexponential response. The former was explained by emission from deep donors at E-c-0.37eV, and the latter by emission from surface states. Capture transients with stress-dependent capture barriers were also observed. An x-ray photoelectron spectroscopy (XPS) study indicated that 0.37 eV-deep donors are N-vacancy related. On the other hand, no current transients took place in N-2 plasma treated and Al2O3-passivated samples. Temperature dependences of I-V curves of Schottky diodes were extremely small and reverse currents were anomalously large. They were explained by the "thin surface barrier" (TSB) model where thermionic field emission and field emission through the TSB region formed by deep donors produce leakage current paths. By combining the results on gateless HFETs and Schottky diodes, a new unified model of near-surface electronic states for the free surface and Schottky interface of AlGaN is proposed. It consists of a U-shaped surface state continuum and N-vacancy related near-surface discrete deep donors. The model can explain the observed large gate leakage and drain current collapse in AlGaN/GaN HFETs in a unified way. It is also shown that our novel Al2O3 passivation, when also used as a gate insulator, can completely suppress current collapse and gate leakage. (C) 2003 American Vacuum Society.