Abstract
It is widely known that the band edge photoluminescence (PL) intensity of MOVPE-grown AlGaAs decreases rapidly below that of comparable LPE-grown material for MOVPE growth temperatures below 780°C. This paper demonstrates that most of the lost intensity can be recovered in low pressure (LP) MOVPE by the use of a high substrate misorientation from {100}. AlGaAs (25% Al) was grown at 700°C on a GaAs lenticular substrate at 30 Torr. PL spectra for the AlGaAs film were taken as a function of substrate misorientation. The band edge intensity was found to be strongly misorientation dependent, with minimum intensity at 2° –3° of misorientation (a commonly used MOVPE misorientation) and maximum intensity at greater than 10° of misorientation. The maximum to minimum intensity ratios were 1000 at 77 K and 50 at 300 K. AlGaAs grown at a misorientation of 2°-3° or less had moderate band edge intensity with considerable deep level emission, whereas at high misorientation only band edge emission was observed. The 300 K PL intensity enhancement of 50-fold with high misorientation is approximately what is lost in reducing the growth temperature (700°C versus 780°C) on nominal {100} substrates using conventional TMGa, TMAl and arsine sources. These results suggest that AlGaAs with high optical quality can be grown at reduced growth temperatures by LP MOVPE if high substrate misorientations are employed. This paper also reports the observation of extended regions of {100} facets with dimensions on the order of a micron for AlGaAs grown on a GaAs lens by LP MOVPE. The regions of long-range morphological ordering appear as a “cat's eye”-shaped feature and for representative growth conditions cover the area with misorientation less than 4.5° from {100}. The long-range ordering in morphology does not appear to originate from nucleation flaws, a case reported previously for atmospheric pressure MOVPE.
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