A new type of optical transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction-band electron wave function, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption for two structures with 65-Å-thick- and 82-Å-thick wells. The transitions exhibit resonant energies of 152 and 121 meV respectively, full width at half-maximum linewidths as narrow as 10 meV at room temperature, and an oscillator strength of 12.2. The material is anticipated to have subpicosecond relaxation times and be ideal for low-power optical digital logic.
The first GaInAsSb/AlGaAsSb diode lasers with a quantum-well active region have been demonstrated. These devices, which were grown by molecular beam epitaxy, emit at ∼2.1 μm. For room-temperature pulsed operation of lasers 100 μm wide, threshold current density as low as 260 A/cm2 and differential quantum efficiency up to 70% have been obtained for cavity lengths of 2000 and 300 μm, respectively. One device 100 μm wide and 1000 μm long has operated pulsed at heatsink temperatures up to 150 °C, with a characteristic temperature of 113 K between 20 and 40 °C. For another device of the same dimensions, cw output power up to 190 mW/facet has been achieved at a heatsink temperature of 20 °C. These characteristics represent a dramatic improvement in performance over double-heterostructure GaInAsSb/AlGaAsSb diode lasers.
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