Minority carrier lifetime and luminescence in MOVPE-grown (Al,Ga)As epilayers and DH lasers

Abstract

Minority carrier lifetime measurements on MOVPE-grown GaAs and Al x Ga 1− x As ( x ≲ 0.17) are reported and compared with similar data on LPE material. Two types of measurements are used. (i) Decay of the band edge luminescence, as optically excited by the 647.1 nm radiation of a mode-locked Kr + laser. This decay yields the effective minority carrier lifetime τ eff at low excitation conditions (δ n, δ n < n 0, p 0); that is, both the radiative and non-radiative part contribute to τ eff. (ii) A novel way of analysing efficiency and light-output data of double-heterostructure lasers operating in the spontaneous high-injection regime (δ n ⋍ δ p > n 0, p 0). With this method, the non-radiative part of the carrier lifetime can be obtained, even when the radiative recombination rate largely exceeds the non-radiative rate. No essential differences in carrier lifetime were found between MOVPE and LPE-grown material. In GaAs, the value of τ eff measured at low excitation densities apparently is limited by the radiative lifetime. The value of τ eff strongly decreases, however, with increasing Al content, showing that effective killer centres are incorporated both during LPE and MOVPE. The recombination through these centres shows saturation effects with increasing excitation densities. It is shown, that ∼10 ppm of water vapour in the reactor during MOVPE has strong adverse effects on the luminescence quality of the (Al, Ga)As as well as on the steepness of the Al gradient in DH structures. High laser threshold currents observed in DH lasers grown under such conditions are related to losses due to superlinear carrier leakage from the active layer to the (Al, Ga)As confinement layers. Finally it is shown that with ample care taken to reduce water and oxygen concentrations during MOVPE, DH lasers operating at 775 nm can be made having nearly the same laser threshold current density as state-of-the-art LPE grown lasers.