Raman study of the vibrational modes in ZnGeN2 (0001)

Abstract

A Raman spectroscopy study was carried out for ZnGeN2 with direction of propagation along the (0001) crystallographic direction on hexagonal single crystal platelets obtained by reaction of gaseous ammonia with a Zn-Ge-Sn liquid alloy at 758 • C. The sample geometry allowed measurement of the a2 and a1 Raman modes. First-principles calculations were carried out of the spectra. Measurements with crossed polarizers yielded spectra that agreed well with first-principles calculations of the a2 modes. Measurements with parallel polarizers should in principle provide the a1L modes. However, for most of the Raman modes, the LO-TO splitting was calculated to be very small, and for the few modes which were predicted to have larger LO-TO splittings, the LO mode was not observed. This absence is tentatively explained in terms of overdamped LO-plasmon coupling. LO-TO mode crossing was identified by comparing the calculated eigenvectors and intensities of individual modes. Some features in the experimental spectra were identified as arising from critical points in the phonon density of states and are indicative of the degree of disorder on the cation lattice.

Growth of Epitaxial ZnSnxGe1−xN2 Alloys by MBE

“…However, the relatively low temperature of 250 °C can limit the potential to obtain a perfectly ordered crystal. Sharp, well-defined Raman peaks have been observed from crystalline ZnGeN 2 needles and platelets grown at 750 °C and higher temperatures 18 , 19 , 25 , 26 , suggesting that higher cation ordering might be achieved through the MBE growth of ZnSn x Ge 1−x N 2 samples at higher temperatures than used herein, if thermal expansion coefficients allow for such on suitable substrates. Investigations utilizing higher temperature growth may reduce point defects and strain, with enhancement of optoelectronic properties, and enable the development of material suitable for use in high-performance devices.…”

“…The broad ZnSn x Ge 1−x N 2 peaks indicate that the bond vibrations probed are not well ordered, representing non-periodicity in the lattice 16 that may result from random cation positioning 17 – 19 . Studies of plasma-assisted vapor-liquid-solid growth of ZnSnN 2 at 485 °C resulted in similarly broad Raman peaks, with the broad peaks attributed to imperfect lattice ordering 16 such as cation anti-site defects 18 – 20 .…”

Band Gaps, Band‐Offsets, Disorder, Stability Region, and Point Defects in II‐IV‐N2 Semiconductors

“…Very recently we also studied BeGeN 2 and BeSiN 2 's electronic band structure and phonons . BeSiN 2 has been synthesized and its band structure was previously studied at the LDA level by Shaposhnikov et al and Huang et al Experimental studies of the Raman spectra have been reported for ZnGeN 2 , and an infrared study of the phonons in ZnSiN 2 was reported by Mintairov et al and analyzed somewhat differently in ref. .…”

Experimental determination of the valence band offsets of ZnGeN2 and (ZnGe)0.94Ga0.12N2 with GaN

“…MOCVD growth of (ZnGe) 1−x Ga 2x N 2 thin films on c-and r-plane sapphire as well as GaN/c-sapphire was also reported [19]. Experimental investigations of ZnGeN 2 have mainly focused on the morphological [5,[16][17][18][19], optical [3,5,16,17,20], crystal structural [5,7,[16][17][18][19][20][21], and lattice vibrational properties [21][22][23]. Deeplevel defects in MOCVD-grown ZnGeN 2 films on sapphire substrates have also been investigated [24].…”