STUDY ON GROWTH AND MATERIAL PROPERTIES OF METASTABLE NITRIDE ALLOY SEMICONDUCTORS

研究了以GaPn合金为代表的III-V-N型氮化物合金半导体的生长和材料性能。这组合金半导体由于极端不相容而很难生长。1.GaPN合金的生长：明确了二甲肼金属有机气相外延生长GaPN合金的生长特征。生长表面N原子物种的脱附对合金成分有很大影响。基于这些生长特性，已经成功地获得了N浓度高达6%的GaPn合金。2.辐射级的来源和性质：从吸收、光致发光和激发光谱等光学测量和分析中发现，辐射级来自于在能带边缘的态密度尾部形成的准局域能级。低温下激发载流子的驰豫过程是由N浓度低于1%时通过N-N对能级的辐射跃迁和N浓度高于1%时的非辐射能级和准局域能级的弛豫控制的。3.带边随N浓度的变化：GaPn合金的带边来源于基质GaP晶体中孤立的-N能级。阐明了准局域激子的迁移率边行为。这些发现与基于紧束缚方法的能带理论计算非常一致，并表明GaPn能隙的成分依赖性中的巨大弯曲是GaPn以及其他相关氮化物合金如GaAsPn和InGaPn的本征性质。

Growth and material properties of nitride alloy semiconductors of the type III-V-N,where GaPN alloy is the representative, have been investigated. This group of alloy semiconductors had been hard to grow due to their extreme immiscibility. The present research project achieved the following major results, which will lead to new technological applications.1.Growth of GaPN Alloys : The growth characteristics of GaPN alloy by metalorganic vapor phase epitaxy using dimethylhydrazine have been clarified. The alloy composition is much affected by the desorption of N atom species from growing surface. Based on these growth characteristics, GaPN alloys with the N concentration as much as 6% have been successfully attained.2.The Origin and Property of Radiative Levels : From optical measurements and analyzes like absorption, photoluminescence and excitation spectroscopies, the radiative levels have been found to originate from the quasi-localized levels formed in the density-of-states tails at the band edge. The relaxation process of excited carriers at low temperatures is governed by the radiative transitions via N-N pair levels for N concentrations below 1%, and by the relaxation to nonradiative and then to quasi-localized radiative levels for the N concentrations above 1%.3.Evolution of Band Edge with Increasing N Concentration : It has been that the band edge of GaPN alloys originates from the isolated-N levels in the host GaP crystal. The behavior of mobility edge for quasi-localized excitons has been clarified. These findings are much consistent with a theoretical calculation for the energy bands based on the tight-binding method, and suggest that the huge bowing in the composition dependence of the GaPN energy gap is an intrinsic property of GaPN as well as other related nitride alloys such as GaAsPN and InGaPN.