Abstract

We earlier reported room temperature pulsed operation of ${\text{Ga}}_{0.84}{\text{In}}_{0.16}{\text{As}}_0{{}_{.}}_{15}{\text{Sb}}_{0.85}/\text{A}{\ell }_{{\text{x}}_{\text{c}}}{\text{Ga}}_{1-{\text{x}}_{\text{c}}}{\text{As}}_{0.04}{\text{Sb}}_{0.96}$ 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 x_c, the Aℓ content of the confinement layers, and on the active layer thickness d_act (see Figure 2). For x_c = 0.27 (DH-I) the lowest threshold, J_th = 7 kA/cm², is obtained with an active layer thickness d_act = 0.8–1 µm. The best result for x_c = 0.34 (DH-II) is J_th ⁼ 3.5 kA/cm² and occurs for d_act = 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 values^4,5 of the refractive indices for the active and confinement materials, n_act and n_conf, support this hypothesis. The confinement is weak because of the small index difference. It is improved and the optimal active layer thickness reduced when n_conf is lowered, which occurs when x_c is increased. However further increase of x_c does not result in lower thresholds: two DH-III type wafers (x_c = 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.

© 1987 Optical Society of America