Low Threshold Current Density 2.2 µm GaInAsSb/AℓGaAsSb Double Heterostructure Lasers

Abstract

We earlier reported room temperature pulsed operation of Ga0.84In0.16As0.15Sb0.85/AℓxcGa1−xcAs0.04Sb0.96 double heterostructure injection lasers (Fig. 1a) with an emission wavelength of 2.2 µm.1,2,3 The wafers were grown by liquid phase epitaxy (LPE) at ~ 530 °C, and their broad area threshold current densities, depend on xc, the Aℓ content of the confinement layers, and on the active layer thickness dact (see Figure 2). For xc = 0.27 (DH-I) the lowest threshold, Jth = 7 kA/cm2, is obtained with an active layer thickness dact = 0.8–1 µm. The best result for xc = 0.34 (DH-II) is Jth = 3.5 kA/cm2 and occurs for dact = 0.5–0.6 µm. The large values of the optimal active layer thickness suggest that there might be less optical confinement in these lasers than in GaInAsP/InP lasers. Estimates of the radiation confinement factor, using calculated values4,5 of the refractive indices for the active and confinement materials, nact and nconf, support this hypothesis. The confinement is weak because of the small index difference. It is improved and the optimal active layer thickness reduced when nconf is lowered, which occurs when xc is increased. However further increase of xc does not result in lower thresholds: two DH-III type wafers (xc = 0.4) gave thresholds of 3.7 and 8 kA/cm2, respectively. This we attribute to too high a lattice mismatch of the confinement layers with respect to the active layer and the substrate, resulting from the difficulty of incorporating enough As into the AℓGaAsSb layer to make it lattice-matched to GaSb.