Abstract

We report the observation of room-temperature optical nonlinearities near 970 nm in InAs/GaAs short-period strained-layersuperlattices (SPSLSs) grown by migration-enhanced epitaxy on GaAs substrates. A typical sample structure consists of six repetitions of two monolayers of InAs and five monolayers of GaAs; this sequence is followed by 25 nm of GaAs, and the entire structure is repeated 50 times. Room-temperature absorbance measurements show clearly resolved excitonic features, and time-resolved photoluminescence indicates a carrier lifetime approaching a nanosecond in these samples. Nonlinear transmission and degenerate four-wave mixing (DFWM) measurements were made with a synchronously mode-locked Styryl 13 dye laser, which produced pulses of 4 ps duration tunable over 950-990 nm. Strong bleaching of the n = 1 heavy-hole excitonic absorption and a large DFWM signal associated with this absorption change were observed. Specifically, a differential transmission (ΔT/T) of 0.43 was measured for a peak pump irradiance of approximately 35 MW/cm². For the same excitation conditions, the DFWM diffraction efficiency was approximately 4 × 10^-4. Measurements were made as a function of wavelength, time delay between the pumps and probe, and pump fluence for several distinct structures. The strengths of the nonlinearities and the carrier dynamics in the various structures will be discussed.

© 1990 Optical Society of America