Temperature-Dependent Photoluminescence of ZnO Thin Films Grown on Off-Axis SiC Substrates by APMOCVD

The growth of high-quality ZnO layers with optical properties congruent to those of bulk ZnO is still a great challenge. Here, for the first time, we systematically study the morphology and optical properties of ZnO layers grown on SiC substrates with off-cut angles ranging from 0° to 8° by using the atmospheric pressure meta–organic chemical vapor deposition (APMOCVD) technique. Morphology analysis revealed that the formation of the ZnO films on vicinal surfaces with small off-axis angles (1.4°–3.5°) follows the mixed growth mode: from one side, ZnO nucleation still occurs on wide (0001) terraces, but from another side, step-flow growth becomes more apparent with the off-cut angle increasing. We show for the first time that the off-cut angle of 8° provides conditions for step-flow growth of ZnO, resulting in highly improved growth morphology, respectively structural quality. Temperature-dependent photoluminescence (PL) measurements showed a strong dependence of the excitonic emission on the off-cut angle. The dependences of peak parameters for bound exciton and free exciton emissions on temperature were analyzed. The present results provide a correlation between the structural and optical properties of ZnO on vicinal surfaces and can be utilized for controllable ZnO heteroepitaxy on SiC toward device-quality ZnO epitaxial layers with potential applications in nano-optoelectronics.

Lattice Monte Carlo model of Langmuir evaporation of ABsemiconductors

Целью работы являлось изучение процессов, протекающих при ленгмюровском испарении подложек полупроводников AB. Предложена и реализована решеточная Монте-Карло модель ленгмюровского испарения GaAs и InAs. Моделирование высокотемпературных отжигов проводилось на базе программного комплекса SilSim3D. В модели учтены процессы образования и диссоциации молекулярного мышьяка и формирования капель металла. Выделены области температур, при которых происходило конгруэнтное и неконгруэнтное испарение. Показано, что температура конгруэнтного испарения на поверхности (111)B ниже, чем на (111)A. На поверхностях (111)А образование капель начиналось вблизи ступеней вицинальных поверхностей, а на (111)B капли образовывались случайным образом на террасах. Purpose. The aim of the work is to study the processes occurring during the Langmuir evaporation of ABsemiconductor substrates. Methodology. The study of GaAs and InAs Langmuir evaporation was performed with the help of Monte Carlo simulation method. Simulation of high-temperature annealing was carried out on the basis of the SilSim3D software complex. The paper presents the abilities of the “Substrate Generator” software complex programs by which the model objects creation and the computing experiments results analysis were carried out. The four-component system, consisting of metal atoms (gallium or indium) in the solid and liquid phases and arsenic in the atomic and molecular form, was considered. The model takes into account the metal droplets formation and the processes of creation and dissociation of molecular arsenic. Each of the processes is characterized by its activation energy. The choice of the model parameters is based on the agreement between simulated and experimental temperature dependences of equilibrium pressure of semiconductor components and arsenic solubility in the liquid metal (gallium, indium) of GaAs and InAs systems over a wide temperature range. Findings. For two surfaces orientations of the model substrates ((111)A and (111)B), the temperatures regions of congruent and incongruent evaporation were determined. It was shown that the temperature of congruent evaporation on the (111)B surface is lower than on (111)A. On the (111)A surfaces, droplet formation starts near the steps of the vicinal surfaces and on (111)B droplets are formed uniformly on the terraces. Value. The obtained model results on the GaAs Langmuir evaporation agree with known experimental data. The results on InAs evaporation leads to the prediction for future experiments.