A Study on Fast Visible-Light Photodetectors Employing Indium Gallium Nitride

目的是通过制造具有高灵敏度和高速响应的器件来表征氮化铟镓薄膜作为光电探测器的材料。这个想法是基于对传统研究过于强调这种材料系统的发光装置的观察。在器件制造中，金属-半导体-金属结构的大面积探测器已经实现了实际可接受的特性。其特点包括在10V下小于100pa的低暗电流，超过0.1 a /W的高响应率，以及10 ns数量级的脉冲响应，检测面积可达1 mm平方。在GaN/蓝宝石表面制备的x=0.12的In_xGa_<1-x>N薄膜在400-500 nm波长范围内具有光活性，通过检测前后入射结构的差异，特别是对电极金属下方区域的照射效果。观察结果发现了薄InGaN对GaN层的异常偏置依赖，这可以解释为在相干生长的InGaN层的扭曲晶体中存在内置场。该效应成功地应用于一个双色探测器，该探测器可以通过改变肖特基势垒二极管的偏置电压来选择性地检测350 nm或400 nm的光信号。此外，通过对层厚度和工作电压的设计，我们实现了具有类似结构的紫外盲蓝光探测器。与响应速度相关，在GaN晶体中进行了深能级测量，发现了一个电子陷阱。然而，这一发现并没有达到消除光电流响应中缓慢成分的实际价值。本研究将继续表征材料系统，并将其应用于实际光电探测器，重点是在薄InGaN层中使用内置场。

The objective is characterizing thin films of indium gallium nitride as a material for photodetectors through fabrication of devices with high sensitivities and high speed responses. The idea was based on the observation that conventional studies placed too much emphases on light-emitting devices of this material system.In the device fabrication, practically acceptable characteristics have been achieved in large area detectors of a metal-semiconductor-metal structure. The characteristics include a low dark current of less than 100 pA at 10V, a high responsivity over 0.1 A/W, and pulse responses on the order of 10 ns, with detecting area up to 1 mm square. The In_xGa_<1-x>N films with x=0.12 on GaN/sapphire were characterized as a photoactive material in the wavelength range of 400-500 nm by examining the differences between front vs. back incidence configurations, especially an effect of illuminating the region just beneath the electrode metal. The observation resulted in finding an anomalous bias dependence of thin InGaN on GaN layers, which is explained by a built-in field existing in a distorted crystal of coherently grown InGaN layer. The effect was successfully applied in a two-color detector that can selectively sense optical signals of 350 nm or 400 nm by simply changing the bias voltage of the Schottky barrier diode. In addition, designing the thicknesses of layers and the operating voltage enabled us to realize a UV-blind blue light detector with similar structure. In relation to the response speed, measurements on deep energy levels were conducted finding an electron trap in the GaN crystal. This finding, however, did not reached to the practical merit of eliminating slow components in photocurrent responses.This study is continued to characterize the material system and apply it to practical photodetectors with an emphasis on the use of built-in field in the thin InGaN layer.