Metal–Organic Chemical Vapor Deposition Growth of ZnGeN₂ Films on Sapphire

Abstract

Heterovalent ternary ZnGeN2 thin films were grown on c-, r-, and a-sapphire substrates using metalorganic chemical vapor deposition. The crystal structure of the films was identified by X-ray diffraction spectroscopy. It is consistent with orthorhombic Pna21 assuming perfect ordering of the cations. For a fully disordered cation sublattice, the X-ray diffraction spectra correspond to a wurtzitic crystal. The growth directions were determined to be along the c-axis for the films grown on c- and a-sapphire substrates, and along the orthorhombic [010] axis (wurtzite[112̅0]) for films grown on r-sapphire substrates. The Zn/Ge atomic ratios, determined by energy dispersive X-ray spectroscopy, were observed to decrease as growth temperatures were increased. Growth rates for all substrates decreased by approximately 10% with changes in growth temperatures from 600 to 710 °C. Broad photoluminescence peaks at ∼2.05 eV were observed at room temperature. These are associated with transitions involving deep level defects. Room temperature photoluminescence excitation spectra showed peaks at ∼3.4 eV associated with enhanced absorption near the band gap of the orthorhombic Pna21 phase. Broad tails in the excitation spectra observed to persist to approximately 2.8 eV may be band tailing due to disorder on the cation sublattice. The unintentionally doped films are n-type with carrier concentrations varying from 2 × 1018 cm–3 to 2 × 1019 cm–3, decreasing with the increase in growth temperature. Room temperature Hall mobilities of up to 17 cm2/V·s were obtained.

Metal–Organic Chemical Vapor Deposition of ZnGeGa2N4

“…The broad double peak centered at 2 eV photon energy is attributed to luminescence from a broad band of radiative defects in the gap. Similar defect PL, referred to as “yellow band” PL, is commonly observed for GaN, and also seems to be a common feature for ZnGeN 2 , whether synthesized by MOCVD, , vapor–liquid–solid growth, hydrothermal-ammonolysis synthesis, or the gas reduction nitridation of ZnO and Ge 2 , and for both ZnGeN 2 and ZnGeN 2 –GaN alloys produced by powder synthesis . Defect PL was detected only for our MOCVD samples grown on r -sapphire substrates at 700 °C; sample G had the highest efficiency PL of all samples examined.…”

“…Growth rates for MOCVD growth of ZnGeN 2 on r -, a -, and c -plane sapphire in this instrument, over roughly the same temperature range, were observed to be much less dependent on temperature at the higher end …”

“…Zhu et al reported low-pressure growth for temperatures between 550 and 700 °C using diethyzinc (DEZn), germane (GeH 4 ), and ammonia (NH 3 ) . Misaki et al reported an optimal growth temperature of 775 °C using DEZn, monomethylgermane, and nitrogen activated by 2.45 GHz microwave radiation. , Karim et al recently reported growth of ZnGeN 2 over the temperature range from 600 to 710 °C, in the same instrument as that employed here, using DEZn, germane, and ammonia …”

Utilizing Site Disorder in the Development of New Energy-Relevant Semiconductors

“…61,78 Additionally, the Zn(Sn,Ge)N 2 system has already demonstrated full miscibility and can be heteroepitaxially grown by both MBE and MOCVD. 73,77,91,92 The integration of II−IV− N 2 materials with established GaN systems removes the doping consideration which often stalls the advancement of new materials; in a hybrid III−N/II−IV-N 2 system, carrier injection will occur through GaN n-and p-type layers to ideally intrinsic II−IV−N 2 emitters. This is advantageous considering the selfcompensating nature of heterovalent ternary compounds.…”

“…Figure5bshows room-temperature photoluminescence (PL) of RF sputter deposited thinfilm ZnGe(O,N) 2 , while Figure5cshows low-temperature (4 K) PL of bulk VLS grown material 61,78. Additionally, the Zn(Sn,Ge)N 2 system has already demonstrated full miscibility and can be heteroepitaxially grown by both MBE and MOCVD 73,77,91,92. The integration of II−IV− N 2 materials with established GaN systems removes the doping consideration which often stalls the advancement of new materials; in a hybrid III−N/II−IV-N 2 system, carrier injection will occur through GaN n-and p-type layers to ideally intrinsic II−IV−N 2 emitters.…”