Characterization of impurity levels in III-Nitrid semiconductors

氮化半导体由于具有宽直接带隙、高击穿电压、高电子饱和速度、高导热性和高热稳定性等优点，在短波长发光器件、高温、大功率高频器件等领域具有广泛的应用前景。尽管iii -氮化物半导体的晶体生长技术取得了显著的进步，但对iii -氮化物半导体中的掺杂和深层缺陷仍未完全了解。了解iii -氮化物半导体中天然缺陷和杂质的来源和作用是非常重要的，因为这些点缺陷直接影响器件的性能。本工作的目的是表征iii -氮化物半导体中深层缺陷的光学和电学性质之间的相关性，并讨论它们的起源。在这项工作中，我们建立了高温电容瞬态光谱系统，以表征氮化镓中隙附近的更深能级。我们还通过开发的测量系统表征了mocvd生长的GaN层的深层水平。在2.0 ~ 2.5 eV范围内，两种GaN样品的光电电容均有增加。这是由于与黄色发光（YL）相关的深层载流子的光电离。此外，还在1.8 ~ 3.4 eV范围内进行了光离后的瞬态电容测量。当光子能量分别为2.1 eV和3.4 eV时，观察到明显的瞬态电容，这两个光子能量分别对应于室温下与YL相关的深能级和GaN的带隙能量。利用等温电容瞬态光谱（ICTS）分析发现，由于ICTS信号为负，深阱能级为少数载流子阱。

III-nitride semiconductors have attracted much attention as promising materials for applications to short wavelength light-emitting devices, high temperature and high power and high frequency devices because of their superior properties, such as wide direct bandgap, high breakdown voltage, high electron saturation velocity, high thermal conductivity and high thermal stability. Despite the remarkable progress in crystal growth technique for III-nitride semiconductors, the doping and the deep-level defects in III-nitride semiconductors are still not fully understood. It is important to understand the origin and role of native defects and impurities in III-nitride semiconductors, because these point defects directly influence on device performance. The objective of this work is to characterize the correlation between optical and electrical properties of the deep-level defects in III-nitride semiconductors and to discuss their origins.In this work, we have built the high-temperature capacitance transient spectroscopy system in order to characterize the deeper levels near the mid gap in GaN. We have also characterized the deep levels in the MOCVD-grown GaN layers by the developed measurement system. The increase in the photocapacitance was observed in both GaN samples in the range of 2.0 to 2.5 eV. This is due to the photoionization of carriers from the deep levels associated with the yellow luminescence (YL). In addition, the transient capacitance measurements after the photoionization were also performed in the range of 1.8 to 3.4 eV. The notable transient of capacitance was observed at the photon energies of about 2.1 eV and 3.4, which are correspond to the deep levels associated with YL and bandgap energy of GaN at room temperature, respectively. By using the isothermal capacitance transient spectroscopy (ICTS) analysis, it is noted that the deep trap levels is the minority carrier trap, because of the negative ICTS signals.