射频等离子体辅助MBE生长GaN及Mg掺杂的光致发光

Photoluminescence Lines in Unintentionally Doped and Mg-doped GaN Grown by Plasma-assisted Molecular Beam Epitaxy

采用射频等离子体辅助分子束外延(RFplasma-assistedMBE)系统生长非故意掺杂GaN和p型GaN,并且通过室温和低温光致发光(PL)谱测试研究了材料的发光特性及与杂质态的关系,对于GaN外延层出现的黄带发光进行分析。结果表明,富Ga条件下生长的GaN材料特性要优于富N生长的材料;非故意掺杂的富Ga样品中出现的黄带发光(YL)与GaN中生成能最低的氮空位(VN)缺陷有关;不同的Mg掺杂浓度对样品的PL特性有较大的影响;结合Hall效应测量结果,认为在Mg重掺杂的样品中出现的黄带发光,与GaN的自补偿效应以及重掺杂导致的晶体质量下降有关。

The optical properties of GaN-based materials are essential to the optoelectronic devices such as light emitting diodes and laser diodes in visible and ultraviolet regions. In this work unintentionally doped GaN and Mg-doped p-GaN were grown on sapphire substrates by plasma-assisted molecular beam epitaxy （PA- MBE）. The photoluminescence （PL） characteristics were studied by means of RT and low-temperature PL spectra with λex = 325 nm. The electrical properties of GaN： Mg were tested by Hall measurement. We especially studied the yellow luminescence （YL） observed in PL spectra in view of the difference between these two types of GaN. In as much as the exciton peaks of Ga-rich GaN exhibit a narrower FWHM than N-rich GaN, it is indicated that material quality of the former is better than the latter. The YL in Ga-rich GaN is related to point defects which is correlative with nitrogen vacancies. Mg doping concentration has a great effect on PL characteristics of p-GaN. The p-type samples show three shapes of PL lines with Mg-doping temperature varying. Hall measurements show that hole concentration of p-type GaN is increased up to a upper limit and then decreased along with the increasing of Mg doping temperature. In combination with the results of hall test, we proposed that the YL in highly Mg-doped GaN could be attributed to self-compensation effect and the decrease of crystal quality caused by highly Mg doping. Through the study, we found that the YL originates from different sources by comparing the undoped GaN and Mg-doped GaN, and it also correlates with the material qualities commonly.