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Surface spatial profiles of defects in GaN

机译：GaN中缺陷的表面空间分布

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Surface profiles of deep levels in GaN sample grown by metal-organic chemical vapor deposition and by hydride vapor phase epitaxy are measured by differential deep level transient spectroscopy (DDLTS). The concentration of acceptor defects at the surface are expected to be lower than the bulk defect concentration because of the shift in Fermi level at the surface, based on theoretical estimates of defect formation energies and the band bending at the surface from spontaneous polarization. Similarly, donor defects are expected to increase in concentration as the surface is approached. The measured concentration profiles of various traps are found to span the range of behavior, from constant, to increasing or decreasing at the interface. Deep level profiling is therefore seen as an important tool to assist in determining defect composition. Although the behavior is as expected, the change in concentration from bulk to surface, is larger than measured values for the defects with the lowest formation energies, based on a conservative estimate of band bending. The difference may reflect a band bending that is different at the growth temperature than predicted, or a consequence of non-equilibrium growth conditions. As growth proceeds, the defects incorporated at the surface are in a non-equilibrium concentration when covered by subsequent layers, unless there is a mechanism whereby equilibrium defects can be formed, e.g. V_(Ga) by forming interstitial Ga, or there is enough energy for defect diffusion to take place. Peaks in the defect profile were measured, as would be expected for a donor defect formed at the surface, but with a non-equilibrium concentration in the bulk, driving diffusion toward the surface.
机译：通过金属有机化学气相沉积和氢化物气相外延生长的GaN样品中深能级的表面轮廓通过差分深能级瞬态光谱（DDLTS）测量。根据缺陷形成能和表面自发极化引起的能带弯曲的理论估计，由于表面上的费米能级移动，预期表面上的受体缺陷浓度会低于体缺陷浓度。同样，随着表面的接近，施主缺陷的浓度有望增加。发现各种陷阱的测得浓度分布范围涵盖行为的范围，从常数到界面的增加或减少。因此，深层次分析被视为帮助确定缺陷成分的重要工具。尽管行为符合预期，但根据带弯曲的保守估计，从体积到表面的浓度变化要比具有最低形成能的缺陷的测量值大。该差异可能反映了在生长温度下与预测温度不同的能带弯曲，或者是非平衡生长条件的结果。随着生长的进行，除非存在可以形成平衡缺陷的机理，例如，由后续层覆盖，在表面处结合的缺陷处于非平衡浓度。通过形成间隙Ga来形成V_（Ga），或者存在足够的能量来进行缺陷扩散。如在表面形成的供体缺陷所预期的那样，测量了缺陷轮廓中的峰值，但是在主体中具有非平衡浓度，从而驱使扩散向表面。

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