p型层结构与掺杂对GaInN发光二极管正向电压温度特性的影响

在温度变化时, 如果GaInN发光二极管能够保持相对稳定的工作电压对其实际应用具有重要意义. 本文通过金属有机化学气相沉积生长了一系列包含不同有源区结构、不同p型层结构以及不同掺杂浓度纵向分布的样品, 并对其在不同温度区间内正向电压随温度变化的斜率(dV/dT)进行了研究. 结果表明: 1)有源区中包括插入层设计、量子阱结构以及发光波长等因素的变化对正向电压随温度变化特性影响很小; 2)影响常温区间(300 K± 50 K)正向电压随温度变化斜率的最主要因素为p-AlGaN 电子阻挡层起始生长阶段的掺杂形貌, 具有p-AlGaN陡掺界面的样品电压变化斜率为-1.3 mV·K^-1, 与理论极限值 -1.2 mV·K^-1十分接近; 3) p-GaN主段层的掺Mg浓度对低温区间(<200 K)的正向电压随温度变化斜率有直接影响, 掺Mg浓度越低则dV/dT斜率越大. 以上现象归因于在不同温度区间, p-AlGaN 以及p-GaN 发生Mg受主冻结效应的程度主要取决于各自的掺杂浓度. 因此Mg掺杂浓度纵向分布不同的样品在不同的温度区间具有不同的串联电阻, 最终表现为差异很大的正向电压温度特性.

Influences of p-type layer structure and doping profile on the temperature dependence of the foward voltage characteristic of GaInN light-emitting diode

Many GaInN light-emitting diodes (LEDs) are subjected to a great temperature variation during their serving. In these applications, it is advantageous that GaInN LEDs have a weak temperature dependence of forward voltage. However, the factors determining the exact temperature dependence of the forward voltage characteristics are not fully understood. In this paper, two series of GaInN LEDs are prepared for investigating the correlation between the epitaxial structural and the temperature dependence of the forward voltage characteristics. The forward voltage characteristics of samples are studied in a temperature range from 100 K to 350 K. The curves of forward voltage versus temperature (dV/dT) are compared and analyzed. For the three samples in series I, according to the barrier thickness and emitting wavelength, they are designated as blue multiquantum well (MQW) with thin barrier (sample A), blue MQW with thick barrier (sample B), and green barrier with thick barrier (sample C) respectively. Their structures of active region including the insertion layer between n-GaN and MQW, the MQW, and the emitting wavelength are different from each other. However, the same slopes of dV/dT at room temperature (300 K± 50 K) are observed in the samples. Moreover, samples B and C with the same p-type layer design also have the same slopes of dV/dT at cryogenic temperatures. Sample A with a much thinner p-type layer shows a lower slope than samples B and C. Based on the these experimental data, it is deduced that the intrinsic physic properties of active region such as structure and emission wavelength have a little influence on the variation of the slope of dV/dT either at room temperature or at cryogenic temperatures. Moreover, the Mg concentration of the p-GaN main region determines the slope of dV/dT at cryogenic temperatures. Low doping concentration leads to a high slope of dV/dT.#br#In order to find the decisive factor determining the slope of dV/dT at room temperature, three samples in series II are grown. For sample E, at the MQW-EBL (electron blocking layer) interface, the Mg concentration increases very slowly while an abruptly varying doping profile is observed for samples D and F. The slopes of samples D and F are both -1.3 mV·K^-1. This is very close to the calculation value of the lower bond for the change in forward voltage (-1.2 mV·K^-1). Meanwhile, the slope of sample E is -2.5 mV·K^-1, which is much higher than those of samples D and F. Thus, it is suggested that the major factor influencing the slope of dV/dT at room temperature is the Mg doping profile of the initial growth stage of the p-AlGaN electron blocking layer. These phenomena are mainly attributed to the changes of the activation energy of p-AlGaN and p-GaN, since it relies on the doping concentration and temperature. Our findings clarify the roles of active region, p-AlGaN and p-GaN in the temperature dependence of the forward voltage characteristic. More importantly, the results obtained in this study are helpful for optimizing the growth parameters to achieve LED devices with forward voltage that has a low sensitivity to temperature.