| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Thursday Sessions |
| Session TF-ThP |
| Session: | Thin Films Poster Session |
| Presenter: | Md Rezaul Karim, The Ohio State University |
| Authors: | M.R. Karim, The Ohio State University B.H.D. Jayatunga, Case Western Reserve University Z. Feng, The Ohio State University M. Zhu, The Ohio State University J. Hwang, The Ohio State University K. Kash, Case Western Reserve University H. Zhao, The Ohio State University |
| Correspondent: | Click to Email |
ZnGeN2 is a wide bandgap material having less than 0.1% lattice mismatch and similar bandgap as GaN [1]. Based on first principles calculations, the valence band maximum of ZnGeN2 is ~1.4 eV above that of GaN at the heterointerface [2]. Such a staggered band alignment between two closely lattice-matched materials has promising applications for novel optoelectronic device designs, for example, high efficiency blue and green light emitting diodes [3]. However, the thin film synthesis of ZnGeN2 is still at an early stage, in contrast to the mature GaN.
Here, we study the growth of ZnGeN2 thin films using metalorganic chemical vapor deposition (MOCVD) and characterization of the crystalline, optical, and electrical properties. Diethylzinc (DEZn), germane (GeH4) and ammonia were used as the precursors for Zn, Ge and N, respectively, and GaN templates and sapphire were used as substrates. The Zn/Ge atomic ratios in ZnGeN2 were determined from energy dispersive X-ray spectroscopy. They were found to decrease with increase in growth temperature (from 600 to 700 °C) but to increase with increase in pressure (from 300 to 500 Torr) and DEZn/GeH4 molar flow rate ratio. The X-ray diffraction 2θ-ω spectra of the ZnGeN2 films are consistent with orthorhombic (perfectly ordered cations) or distorted wurtzite (disordered cations) polymorphs. High resolution scanning transmission electron microscopy imaging was used to investigate the crystalline quality and crystalline structure of the films. The ZnGeN2 films grown on c-sapphire and GaN substrates have planar surfaces from scanning electron micrographs while those on r-sapphire substrate have stepped surface morphologies. A broad peak at ~2.05 eV was observed from room temperature photoluminescence (PL) spectra and is was attributed to transitions involving deep level defects. The PL excitation spectra peaked around 3.4 eV, and is attributed to excitonic enhancement of the absorption near the band gap. The as-grown films were found to be n-type with 1018 -1019 cm-3 carrier concentrations and room temperature mobilities up to 17 cm2/V·s.
In summary, the studies from this work on the MOCVD growth of ZnGeN2 thin films are a step towards the better understanding of this material and thus, towards the implementation of ZnGeN2 for device applications.
Acknowledgements
The authors acknowledge funding support from the National Science Foundation (DMREF-1533957).
References
1. A. Punya, T. R. Paudel, and W. R. L. Lambrecht, Phys. Status Solidi C, 8, 2492 (2011).
2. A. P. Jaroenjittichai, S. Lyu, and W. R. L. Lambrecht, Phys. Rev. B., 96, 079907(E) (2017).
3. L. Han, K. Kash, and H. Zhao, J. Appl. Phys., 120, 103102 (2016).