Abstract

Under certain growth conditions GalnP tends to exhibit spontaneous superlattice ordering with atoms arranging in GaP/lnP monolayers along two of the possible four [111] crystal directions. The superlattice ordering leads to significant changes in the electrical and optical properties of the crystal most prominently decreasing the energy band gap. In ordered material optical transitions between the highest valence band and the conduction band are not allowed for polarisation parallel to the ordering directions. In order to demonstrate the potential device applications of this polarisation effect we have studied the electroluminescence (EL) and the electroabsorption of (Al_0.3Ga_0.7)_0.52In_{0 48}/Ga_{0 52}ln_0.48P p-i-n double hetero structures. Samples with ordered (o-samples) and disordered (d-samples) GalnP active layers have been grown lattice matched to GaAs by metal organic vapour phase epitaxy (MOVPE). The o-samples were grown at 650°C on exactly oriented GaAs substrates while for the d-samples a growth temperature of 710°C and 6° toward [111A] tilted substrates have been used. Moreover, thermal disordering of the o- samples was achieved by rapid thermal annealing (RTA) at 900°C for 30 sec after growth (a-samples). This technique allows to compare ordered and disordered material made from the same epitaxial wafer. Surface emitting light emitting diodes (LED) with chemically dry etched mesas have been fabricated. The EL spectra of o- and a-LED show peaks at 673 nm and 650 nm respectively. This corresponds to an energy shift of 65 meV and is in very good agreement with PL measurements. The a-samples exhibit a significantly decreased EL-efficiency compared to the o-LED which can be explained by damage caused by RTA. Polarisation measurements of o-LEDs exhibit a contrast of 1.4 dB between polarisation parallel to the $\left[01\overline{1}\right]$ and [011] crystal direction respectively. This effect is nearly independent of diode current and mesa geometry, but not observed for a-LEDs. This lifted degeneracy of polarisation states associated with the ordered GalnP phase has to be considered as a very promising feature for polarisation control in VCSELs.

© 1996 IEEE