Epitaxial Growth and Structural Characterization of Single Crystalline ZnGeN 2
- PDF / 901,090 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 55 Downloads / 212 Views
nloaded from https://www.cambridge.org/core. IP address: 80.82.77.83, on 04 May 2018 at 06:46:20, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300002374
This coordination obeys the four electrons per site rule, and the atomic bonding in the crystal is of covalent nature. The transfer from III-V to II-IV-V2 compounds brings about new properties of the materials such as band gap, electronic band structure, and non-linear optical properties caused by the drop in symmetry due to superlattice formation. Chalcopyrite II-IV-As2 and II-IVP2 compounds are relatively extensively investigated in search of superior thermoelectric and non-linear optic materials[5]. An outstanding achievement in chalcopyrite research is the nonlinear optical applications of ZnGeP2 and CdGeAs2[5]. There is little work on II-IV-N2, even including powder synthesis, perhaps due to the need for high temperature and pressure[6,7]. The goal of our research is an exploration of single crystalline II-IV-N2 materials in conjunction with Group III-nitrides and SiC research. Experiment The initial growth experimentation was carried out by microwave plasma enhanced activated nitrogen MOCVD. However, most of the materials reported here have been grown by ammonia source MOCVD. The growth reactor is a water cooled stainless steel vertical chamber, in which the wafer can be rotated to ensure film thickness uniformity. The precursors used as zinc and germanium sources are diethylzinc and germane. Activated nitrogen was supplied from ammonia. Ammonia flow rate was kept at 180 mmole/minute, and total flow rate of diethylzinc and germane was varied around 30 mmole/minute. Corresponding [NH3]/([DEZ] + [GeH4]) ratio is 5000. Crystalline deposition could be obtained with the growth temperature from 550oC to 700oC. During the growth the chamber was kept at a pressure in a range of 40-500 Torr. The substrate used to grow ZnGeN2 was c- and r-plane sapphire, and ZnGeN2 was grown via an intermediate GaN seed layer. Surface morphology of the epitaxial films were examined by photomicroscopy, scanning electron microscopy and atomic force microscopy. Crystallinity of the ZnGeN2 layers was investigated by x-ray diffraction θ−2θ scans, double crystal x-ray rocking curve analysis and reflection high energy electron diffraction images. Results The epitaxial ZnGeN2 layer is smooth, shiny, and the color looks yellowish by visual examination. A scanning electron microscope picture of the surface shows, sometimes, shiny particulates, the size and amount of which is dependent on the DEZ to GeH4 molar ratio, suggesting that it is accumulation of extra zinc. Atomic force microscopy was utilized to examine the surface microscopic structure and roughness. Inclined height images of ZnGeN2 layers grown on c- and r-plane sapphire substrates are shown in Figs. 1a and 1b, respectively. A common feature in the two microscopic pictures is a spike shaped morphology, which demonstrates that the growth is columnar from
Data Loading...
