The ongoing quest for thresholdless semiconductor lasers has led to the development of new materials (e.g., quantum wells, wires, and dots) and new optical resonators (e.g., microdisks and photonic bandgap crystals). Semiconductors are often preferred for lasers and optical devices, because of their high efficiency, high reliability, low cost, and compact size. However, the operating wavelength of semiconductor optical devices is fixed by the bandgap energy. Thus, applications that require wide tunability of the operating wavelength still utilize Nd:​YAG-pumped dye-lasers or titanium-sapphire lasers, and it would be a significant advancement to tune the stimulated emission from a semiconductor over a wide wavelength range.

In this work, we demonstrate the first GaAs deep-center laser with low threshold using electrical injection. This laser, which intentionally utilized gallium-arsenide deep-center transitions, exhibited a threshold of less than 2A/cm² in continuouswave mode at room temperature at the important 1.54μm fiber-optic wavelength. This threshold is three orders of magnitude lower than for bandgap transitions in conventional bulk semiconductors (for which 1kA/cm² is typically required for laser action). It is significant that this first demonstration of broad-area laser action was accomplished with electrical injection, and not merely optical pumping, as is usual for a new material.

Stimulated emission from p-n junctions is also demonstrated with single pass devices fabricated with GaAs deep-center material at electrical injections less than 1A/cm². The room temperature stimulated emission from GaAs deep-centers can be tuned very widely from the bandgap (0.9μm) to half the bandgap (1.6μm) by changing the electrical injection.

To our knowledge, we have made the first measurement of optical gain from GaAs deep-centers. Using a variable stripe length method, the material exhibits a gain as high as 250cm⁻¹ at the 1.3-1.5μm fiber-optic wavelengths in the absence of waveguide confinement. Different types of waveguide designs, slab and DBR waveguides, waveguides with gratings, and circular microresonators were fabricated. Modifications to the fabrication procedures were directed at achieving high quality sidewalls using reactive ion etching. The optical emission from resonant cavities showed enhancements with each iteration of the device design. These devices were pumped either optically or electrically. We measured optical emission as a function of the injection (L-I) to determine laser action in these GaAs deep-center devices. Mode selectivity was found to be an important issue in the demonstration of laser action. This research thus offers a new material for making fiber optic wavelength optical devices.