Influence of polarization fields and depletion fields on photoluminescence of AlGaN/GaN multiple quantum well structures
Influence of polarization fields and depletion fields on photoluminescence of AlGaN/GaN multiple quantum well structures
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DOI：
10.1002/pssb.200301782
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发表时间：
2003-05-01
影响因子：
1.6
通讯作者：
Akasaki, I
中科院分区：
文献类型：
--
作者：
Monemar, B;Haratizadeh, H;Akasaki, I
本文报道了Al_（0.07）Ga_（0.93）N/GaN多量子威尔斯阱（MQW）的低温光致发光（PL）的详细研究。该结构生长在蓝宝石上，具有常规的低温AlN成核层和厚GaN缓冲层。研究了几组5个量子阱的多量子阱样品，其中一组在势垒中掺杂Si达到或超过金属极限。还研究了名义上未掺杂的MQW样品。掺杂样品的光谱行为受到近表面耗尽场的强烈影响，导致来自非等效量子阱的不同光谱的重叠。最接近表面的量子阱在某些样品中可能是不活跃的，由于一个非常高的耗尽场。另一方面，对于未掺杂样品的情况，近表面量子阱是活跃的，并且在PL谱中最突出。来自离散阱宽度变化的结构在这里在PL光谱中被解析。结果表明，对于没有额外的覆盖层的结构的耗尽场和极化场需要考虑在实验数据的解释。理论计算结果与实验结果一致。即使在金属样品的情况下，如观察到的恒定PL衰减时间独立的掺杂，本地化的存在进行了讨论的空穴波函数到AlGaN屏障的渗透。这种本地化也表现在一个相当大的LO声子耦合强度在所有样品的研究。
We report on a detailed study of low temperature photoluminescence (PL) in Al0.07Ga0.93N/GaN multiple quantum wells (MQWs). The structures were grown on sapphire with the conventional low temperature AlN nucleation layer and thick GaN buffer layer. Several sets of 5 QW MQW samples were studied, one set with Si doping in the barriers up to or above the metallic limit. Nominally undoped MQW samples were also studied. The spectral behaviour of the doped samples was strongly affected by the near surface depletion field, causing overlap of different spectra from non-equivalent QWs. The QWs closest to the surface are presumably inactive in some samples, due to a very high depletion field. For the case of undoped samples, on the other hand, the near surface QWs are active and most prominent in the PL spectra. The structure from discrete well width variations is here resolved in the PL spectra. The results demonstrate that for structures with no additional capping layer both the depletion field and the polarisation fields need to be considered in the interpretation of experimental data. The theoretically estimated fields in this work are consistent with the experimental spectra. The presence of localisation even in the case of metallic samples, as observed by a constant PL decay time independent of doping, is discussed in terms of penetration of the hole wave functions into the AlGaN barriers. This localisation is also manifested in a sizeable LO phonon coupling strength in all samples studied.