The ternary ZnMgTe epitaxial layer is promising for application as a cladding layer of ZnTe based pure green light-emitting devices, because of the wider band gap than ZnTe. However, there are only a few papers on ZnMgTe epitaxial layer grown by metalorganic vapour phase epitaxy (MOVPE), which is a potential growth technique for mass production. The systematic study using MOVPE should be done. In this work, we studied the effects of the substrate temperature (Tsub) and the molar ratio of Te/Zn precursors ([Te/Zn]) on the photoluminescence (PL) spectra of undoped ZnMgTe epitaxial layer grown by MOVPE.
Undoped ZnMgTe layers were grown by vertical MOVPE on Ga-doped ZnTe (100) substrates. Dimethylzinc (DMZn), bis-methylcyclopentadienyl-magnesium ((MeCp)2Mg) and diethyltelluride (DETe) were used as source materials. H2 was employed as a carrier gas with the total flow rate of 0.8 slm. The transport rate of (MeCp)2Mg was fixed at 2 µmol/min. The influence of Tsub was studied by varying from 340 to 420°C, when the transport rates of DMZn and DETe were fixed at 15 and 10 µmol/min, respectively. Also, the influence of [Te/Zn] was investigated under the constant DETe transport rate and Tsub. The PL spectra of the epitaxial layers were measured at 4 K using a 457.9 nm Ar ion laser.
In PL spectra of layers grown at Tsub≥380°C, the band-edge emission (peak A) and broad band emission (peak B) located approximately 140 meV below the peak A are clearly observed. On the other hand, layers grown at Tsub≤360°C show only peak B. The peak energies of the peak A and B shift toward high energy side with decreasing Tsub. According to the previous study [1], in which the incorporation efficiency of Mg is related to the premature reaction between DETe and (MeCp)2Mg, lower Tsub may be effective for the increase of the incorporation efficiency of Mg due to the reduction of the premature reaction. The intensity ratio of the peak B to peak A decreases with increasing [Te/Zn], indicating that the optical property of the layer is improved.
This study was partly supported by Industrial Technology Research Grant Program in 2005 from New Energy and Industrial Technology Development Organization (NEDO) of Japan.
[1] K. Saito et. al., J. Crystal Growth 298 (2007) 449.
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