ZnTe is a promising material for pure green light emitting diodes (LEDs). Phosphorus (P) is considered to be a suitable p-type dopant in ZnTe, since the pure green LEDs is obtainable by a thermal diffusion of Al into p-type ZnTe:P. As for metalorganic vapour phase epitaxy (MOVPE), which is a promising growth technique for mass production, we have successfully grown ZnTe:P homoepitaxial layers by MOVPE using tris-dimethylaminophosphorus (TDMAP) as a novel P source. Although the layer with a high carrier concentration of 1.3×1018 cm-3 can be obtained by using this dopant, the photoluminescence (PL) spectrum at 4 K shows only donor-accepter pair emission (DAP). The annealing treatment in N2 flow (ATN) is expected to improve the PL properties of ZnTe:P layers [1]. The effect of ATN should be clarified for ZnTe:P layers grown under various growth conditions. In this study, ATN was adopted for ZnTe:P layers grown at different substrate temperatures.
ZnTe:P layers were grown on semi-insulating (100) ZnTe:Ga substrates in the atmospheric pressure MOVPE system with horizontal reactor. Dimethylzinc (DMZn) and diethyltelluride (DETe) were used as source materials, while TDMAP as a dopant source. H2 was employed as a carrier gas with the total flow rate of 4.8 slm. The substrate temperature was varied from 360 to 500°C, while the transport rates of DMZn, DETe and TDMAP were fixed at 92, 83 and 3 µmol/min, respectively. ATN for the as-grown layers was performed in N2 flow. The optical and electrical properties were investigated in order to assess the effects of ATN.
PL properties at 4 K of the layers are dramatically improved by ATN, i.e. DAP emission vanishes and instead free-to-bound transition emission and broadened acceptor-related excitonic emission appears even for the layers grown at low substrate temperature. PL intensity at room temperature is enhanced remarkably by ATN independent of the substrate temperature. ZnTe:P layer with 3~1018 cm-3 was obtained through this study.
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., Abstracts of E-MRS 2006 Fall Meeting, F-39 (2006).
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