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

目标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材料的特性。这一想法是基于观察到，传统的研究过于重视这种材料系统的发光器件。在器件制造中，实际上可以接受的特性已经在金属-半导体-金属结构的大面积探测器中实现。其特性包括在10 V下小于100 pA的低暗电流，超过0.1 A/W的高响应度，以及10 ns量级的脉冲响应，检测面积高达1 mm 2。在<1-x>GaN/蓝宝石衬底上制备的In_xGa_ N（x=0.12）薄膜在400-500 nm波长范围内具有光活性，通过比较正面入射和背面入射的结构差异，特别是对电极金属正下方区域的照射效果，对薄膜的光活性进行了表征。观察结果发现GaN层上的薄InGaN的异常偏压依赖性，这是由相干生长的InGaN层的扭曲晶体中存在的内建场解释的。该效应已成功地应用于双色探测器中，通过简单地改变肖特基势垒二极管的偏置电压，可以选择性地感测350 nm或400 nm的光信号。此外，通过对膜层厚度和工作电压的设计，我们实现了一种结构相似的紫外盲蓝光探测器。关于响应速度，进行了深能级的测量，发现GaN晶体中存在电子陷阱。然而，这一发现，并没有达到消除光电流responses.This研究中的慢成分的实际优点是继续表征的材料系统，并将其应用于实际的光电探测器，重点是使用内置场在薄InGaN层。

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.