采用C-V法, 根据C-2-V曲线和C-3-V曲线, 并结合C-V幂律指数k, 分析了T=25~-195 ℃温度范围内, 温度变化对GaN基蓝光发光二极管pn结类型的影响。实验结果表明: 当T为25 ℃和-50 ℃时, C-2-V呈明显的线性关系, 同时幂律指数k为0.5, 说明该温度范围内的pn结类型为严格的突变结; 而温度降低至-100 ℃时, k值变为0.45, 说明pn结类型开始发生变化; 当温度继续降低至-150 ℃和-195 ℃时, 幂律指数k分别为0.30和0.28, 说明pn结类型已经发生了变化, 变为非突变非缓变结。造成这一现象的原因是低温导致的载流子冻析效应, 以及晶体的缺陷和界面态形成的局域空间电荷区在低温环境下, 影响了pn结原来的空间电荷分布, 并改变了pn结类型。

Capacitance-voltage(C-V) measurement is a useful method for studying of pn junction. In this paper, the C-V measurement was applied to analyze the influence of temperature on the type of pn junction of GaN-base LED in a temperature range from 25 ℃ to -195 ℃ according to C-2 -V curve, C-3 -V curve and power law index k. The experimental results showed that the change of temperature will have an effect on the structure of junction. When the temperatures are 25 ℃ and -50 ℃, respectively, there was a significant linear relationship for C-2-V, and the index k was 0.5, which indicating an abrupt junction in a temperature range from 25 ℃ to -50 ℃. When the temperature was cooled down to T=-100 ℃, the structural type of pn junction began to change and the index k was 0.45. When the temperature continued to decrease to T=-150 ℃ and -195 ℃, the index k became 0.30 and 0.28, corresponding to a non-abrupt and non-linear junction. The possible explanations of such phenomenon were low-temperature carrier freeze effect, and the localized space charge region produced by crystal defects and interface states. The enhancement of localized space charge region finally affected the structure of pn junction in low temperature environment.