The overflow is enhanced by the high electric field caused by the high resistivity in the p-cladding layer. It increases towards the p-side, as in the hole case. These inhomogeneous injections of carriers will cause inhomogeneous generation of the optical gain. Figure 1 . Leakage current due to the overflow to the p-cladding layer and current injected into the MQW layer as functions of total current.
Leakage starts in the low current region.
Figure 2 . Overflow current as a function of total current at various Al compositions. The current density where leakage starts increases as Al composition increases. We need E g of about 800 meV to sufficiently suppress the leakage current. Figure 3 .