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型氮化合金半导体的生长和材料性能。这组合金半导体由于其极端的不混溶性而难以生长。目前的研究项目取得了以下主要成果，这些成果将导致新的技术应用。GaPN合金的生长：研究了金属有机气相外延法制备GaPN合金的生长特性。生长表面N原子的脱附对合金成分有很大影响。基于这些生长特性，成功制备了含氮量高达6%的GaPN合金。辐射能级的起源和性质：通过光学测量和分析，如吸收光谱、光致发光光谱和激发光谱，发现辐射能级起源于在能带边缘的态密度尾部形成的准局域能级。当N浓度低于1%时，激发载流子的弛豫过程由N-N对能级的辐射跃迁控制；当N浓度高于1%时，弛豫过程由非辐射弛豫到准局域辐射弛豫控制。带边随氮浓度增加的演变：GaPN合金的带边源于基体GaP晶体中孤立的氮水平。阐明了准局域激子的迁移边缘行为。这些发现与基于紧密结合方法的能带理论计算结果非常一致，并表明GaPN能隙的成分依赖性的巨大弯曲是GaPN以及其他相关氮化合金（如GaAsPN和InGaPN）的固有特性。

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.