利用p-n＋结反向I-V特性计算p-GaN载流子浓度的方法

A new method to estimate the p-GaN carrier concentration by analyzing the reversed current-voltage characteristic curve of p-n^+ junction diode

提出了一种利用p-n^+结反向I-V特性随偏压变化的关系计算p-Ga N载流子浓度的方法.研究发现,当p-n^+中的p-Ga N层没有完全耗尽时,反向电流比较小,属于正常的p-n结电流特性,当反向偏压增加到一定值时,p-Ga N层就完全耗尽,p-n^+结特性就变成了肖特基结特性,反向电流显著增加.找到达到稳定反向电流的临界电压值,就可以计算出p-Ga N的载流子浓度.模拟结果验证了这个思想,计算得到的p-Ga N载流子浓度与设定值基本一致.

GaN and its related nitride materials have been investigated for many years due to their extensive applications in semiconductor optoelectronics and microelectronics. The realization of p-GaN plays a key role in developing the GaN- based optoelectronic devices such as light-emittingdiodes, laser diodes and ultraviolet photodetectors. Furthermore, it is very significant to acuurately obtain the carrier concentration value of p-GaN layer for device design and fabrication. Usually the Hall measurements are employed to obtain the hole concentration of p-GaN layer. However, this method is not suitable for very thin samples, especially the p-GaN layer in the device structure, which is commonly very thin. Furthermore, the good Ohmic contact to p-GaN is not easy to realize. In consideration of the importance of p-GaN in determining the performance of GaN-based devices, it is necessary to find other new methods to measure or check the carrier concentration data of p-GaN. In this paper, a new method to estimate the carrier concentration of p-GaN by analyzing the current-voltage characteristic curve of p-GaN/n＋-GaN diode is proposed. The main physical process is as follows： generally the carrrier concentration of p-GaN layer is far less than that of n＋-GaN layer, and the depleted region is mainly located in the p-GaN. When the reversed bias voltage is very small, the diode shows conventional properties of p-n＋ junction and the corresponding reversed current is very low since the p-GaN is not completely depleted. With the increase of reversed bias voltage, the depleted region of p-GaN also increases. Once the p-GaN is completely depleted, the case turns different. The diode will show Schottky junction properties and the corresponding reversed current increases obviously when the p-GaN is completely depleted under a certain reversed bias voltage since the ideal reversed current of Schottky junction is larger than that of p-n＋ junction. The hole concentration could be derived according to the device physics if the bias voltage is discovered, which leads to the properties changing from the p-n＋ junction to conventional Schottky junction. The simulation results confirm the idea, and the calculated p-GaN carrier concentration is almost equal to the originally assumed value. The proposed method is interesting and may be helpful to accelerate the research of p-GaN and related optoeleetronic devices.