High-Performance Uncooled 1.3-µm AlxGayIn1-x-yAs/InP Strained-Layer Quantum-Well Lasers for Subscriber Loop Applications

Design considerations for fabricating highly efficient uncooled semiconductor lasers are discussed. The parameters investigated include the temperature characteristics of threshold current, quantum efficiency, and modulation speed. To prevent carrier overflow under high-temperature operation, the electron confinement energy is increased by using the AlxGayIn1-x-y As/InP material system instead of the conventional GaxIn1-xAsyP1-y/InP material system. To reduce the transparency current and the carrier-density-dependent loss due to the intervalence-band absorption, strained-layer quantum wells are chosen as the active layer. Experimentally, 1.3-µm compressive-strained five-quantum-well lasers and tensile-strained three-quantum-well lasers were fabricated using a 3-µm wide ridge-waveguide laser structure. For both types of lasers, the intrinsic material parameters are found to be similar in magnitude and in temperature dependence if they are normalized to each well. Specifically, the compressive-strained five-quantum-well lasers show excellent extrinsic temperature characteristics, such as small drop of 0.3 dB in differential quantum efficiency when the heat sink temperature changes from 25 to 100°C, and a large small-signal modulation bandwidth of 8.6 GHz at 85°C. The maximum 3 dB modulation bandwidth was measured to be 19.6 GHz for compressive-strained lasers and 17 GHz for tensile-strained lasers by an optical modulation technique. The strong carrier confinement also results in a small k-factor (0.25 ns) which indicates the potential for high-speed modulation up to 35 GHz. In spite of the aluminum-containing active layer, no catastrophic optical damage was observed at room temperature up to 218 mW for compressive-strained five-quantum-well lasers and 103 mW for tensile-strained three-quantum-well lasers. For operating the compressive-strained flve-quantum-well lasers at 85°C with more than 5 mW output power, a mean-time-to-failure (MTTF) of 9.4 years is projected from a preliminary life test. These lasers are highly attractive for uncooled, potentially low-cost applications in the subscriber loop.