Growth temperature effect on MOVPE Si-doped GaN: Thermodynamic modeling

Si-doped GaN layers have been grown using SiN treatment growth by MOVPE on sapphire (0 0 0 1) in a homemade vertical reactor. The growth was monitored by in situ laser reflectometry. The growth temperature was varied between 1090 and 1150 °C, keeping constant all the other parameters. The layers reveal a smooth surface morphology. The room temperature electron concentration is nearly constant about 2×1018 cm−3 with a constant SiH4 flow of 1 nmol/min. The growth rate decreases slowly. Thermodynamic analysis of the growth temperature effect was investigated. To this aim, equilibrium calculations have been performed using the GEMINI code. The experimental growth conditions are used for the calculations. The results show that the important species in the vapor phase are SiNH, SiH4 and SiH2. Two growth regimes are revealed with a critical temperature (Tc) of about 1220 K. For the higher temperature (T>Tc), the partial pressure of SiH4 and SiH2 decreases and increases, respectively, as well as that of SiNH remains constant. We tentatively correlated the experimental and the calculation results based on the fact that the GaN growth temperature is usually higher than Tc. Thus, the evolution of the electron concentration is due to the SiNH species and the growth rate reduction is related to the GaN decomposition. A chemical reaction of the Si-doped GaN with SiH4 as Si precursor is proposed.