Theoretical analysis of lasing characteristics of stacked lnGaN quantum dot lasers from atomic scale

采用<0.2><0.8>极化势相关的sp^3紧束缚方法研究了GaN势垒层中In_ Ga_ N金字塔量子点的电子结构。应变和原子位置的计算采用了Keating势的价力场方法。对于直径为86.4A，高度为20.8A，端面倾角为30 °的量子点，计算出最大压电场为1.64MV/cm。由于量子限制的斯塔克效应，能隙显示出0.100 eV的红移。场导致量子点中电子和空穴波函数的空间分离。估计了能完全屏蔽场的电子-空穴对的数目随粒子直径的变化。我们发现对于直径为86.4A的量子点，需要13个电子空穴对才能完全屏蔽场。在Damilano等人的实验中，在<PL>室温下测得具有相似量子点尺寸的MBE生长的In_<0.2>Ga_<0.8>N量子点的光致发光峰值能量E_1为2.71eV;与棱柱量子点的Eg = 2.502 eV相比，金字塔量子点的Eg = 2.706 eV与测量的能量E_2 = 2.71 eV更好地一致<PL>。

We have analyzed the electronic structures of ln_<0.2>Ga_<0.8>N pyramidal quantum dots (QDs) in a GaN barrier layer using a polarization-potential dependent sp^3 tight-binding method. A valence-force-field method using the Keating potential was used for the strain and atom-position calculations. For the QD with the diameter 86.4 A, height of 20.8 A, and facet inclination angle of 30 degree, the maximum piezoelectric field is calculated to be1.64 MV/cm. The energy gap shows a red shift of 0.100 eV due to the quantum-confined Stark effect. The field causes a spatial separation of the electron and hole wave functions in the QD. The number of electron-hole pairs, which can screen the field totally, is estimated as a function of the diameter. We find that 13 electron-hole pairs are required for the complete field screening for the QD with the diameter 86.4 A. In experiments by Damilano et al., the photoluminescence peak energy, E_<PL>, of 2.71 eV (at room temperature) was measured for the MBE-grown In_<0.2>Ga_<0.8>N QDs with the similar QD size ; diameter = 100 A, heitht = 20 A. Eg = 2.706 eV for the pyramidal QD is in better agreement with the measured energy, E_<PL> = 2.71 eV, than Eg = 2.502 eV for the prismatic QD.