GaN基LED低温空穴注入层的MOCVD生长研究

Investigation of Low Temperature Hole-injection Layer in GaN-based LED Epitaxial Wafer Grown by MOCVD

针对GaN基LED空穴注入效率低的问题,在量子阱与电子阻挡层之间插入低温空穴注入层(LTHIL),实验研究了MOCVD生长LT-HIL时二茂镁(Cp2Mg)流量和生长温度的影响。结果表明:随着Cp2Mg流量的增加,外延薄膜晶体质量下降,外延片表面平整度和均匀性降低;而受Mg掺杂时补偿效应的影响,主波长先红移后蓝移,芯片的输出光功率先升高后降低,正向电压先降低后升高。相比于无LT-HIL的样品,在20mA工作电流下,Cp2Mg流量为1.94μmol/min时制备的芯片的输出光功率提升20.3%,而正向电压降低0.1V。在Cp2Mg流量较大时,LT-HIL的渐变式生长温度对外延质量有所改善,但不是主要影响因素。

A low-temperature hole-injection layer (LT-HIL) was inserted between multiple-quantum well and electron-blocking layer in GaN-based light-emitting diodes (LEDs) to improve the hole-injection efficiency. The effects of magnesocene (Cp2Mg) flow rate and process temperature of LT-HIL in MOCVD epitaxy were investigated. The surface reflectivity and dominant wavelength of epitaxial wafers were measured by photoluminescence spectrometer, the surface profiles were observed by microscope, and the light-output power and forward voltage of fabricated chips were tested by wafer-level auto-measurement system. As the Cp2Mg flow rate increases, the crystal quality, flatness, and uniformity of epilayer decrease. Due to the compensation effects in Mg-doped GaN material, the dominant wavelength shows red-shift at first and then blue-shift, the output power of the chip goes up to the maximum then falls down, and the forward voltage goes down to the minimum then rises up. Compared to conventional LED chips without LT-HIL, the output power and forward voltage of the LED chips with Cp2Mg moral flow rate of 1.94 μmol/min are enhanced by 20.3% and reduced by 0.1 V under the injection current of 20 mA. It is also shown that the gradually changing process temperature can also improve the crystal quality, flatness and uniformity of epilayer, although it is non-principal reason under the condition of large Cp2Mg moral flow rate.