Uniformity of the wafer surface temperature during MOVPE growth of GaN-based laser diode structures on GaN and sapphire substrate

Abstract

Wafer bowing has a strong impact on the wavelength homogeneity of InGaN based light emitters due to the strong temperature dependence of the In incorporation. Using in-situ curvature measurements and pyrometry we have studied the impact of growth conditions on the lateral and vertical temperature distribution across the wafer and on wafer bow on sapphire and GaN substrates. From the pyrometry signal at 950 nm the temperature of the substrate holder can be deduced. Using 400 nm pyrometry the surface temperature was determined for sufficiently thick GaN layers. While total flow and satellite rotation were found to have no impact, the total pressure affects the vertical temperature profile and thus the wafer bow. However, the effect is small and can only be used for fine tuning. To compensate for the strain of the AlGaN cladding layer in laser structures precurved GaN substrates are shown to be advantageous. Photoluminescence confirmed a spatially uniform surface temperature distribution during the deposition of the InGaN quantum well active region with a peak wavelength around 500 nm and a deviation as low as 3.5 nm on flat sapphire substrates and precurved GaN substrates.