Effect of substrate misorientation on the optical properties and hole concentration of Ga 0.5In 0.5P and (Al 0.5Ga 0.5) 0.5In 0.5P grown by low pressure metalorganic vapor phase epitaxy

Abstract

The effect of substrate misorientation on the optical and electrical properties of Ga 0.5In 0.5P and (Al 0.5Ga 0.5) 0.5In 0.5P grown by low pressure metalorganic vapor phase epitaxy has been studied. Undoped (100) GaAs substrates with misorientation angles of 2°, 4° and 6° towards the [111], [11 1 ], [110] and [101] directions were used during the experiments. The surface morphologies appear to be mirror smooth and free of hillocks, using substrates with misorientations towards the [111], [110] and [101] directions. On the [11 1 ] misoriented direction, the epilayers show orange-peel surfaces. The energy band gap, measured from 20 K photoluminescence (PL) spectra for both Ga 0.5In 0.5P and (Al 0.5Ga 0.5) 0.5In 0.5P, increases monotonically with increasing angle of misorientation f or all tilt directions except [11 1 ]. The epilayers grown on substrates with a misorientation of 2° towards the [11 1 ] direction have energy band gaps that are lower than those grown on (100) exact substrates. Further, PL FWHM decreases with increasing off angle for all directions. The epilayers grown on substrates misoriented towards the [111] direction appear to be of high crystal quality since their PL FWHMs are smaller than those grown on (100) exact substrates. Finally, the hole concentration is found to increase with increasing angle of misorientation along the [111], [110] and [101] directions. On the other hand, p-type carrier concentration decreases as the off angle increases along the [11 1 ] direction.