GaAs LEDs with n-i-p-i active layers fabricated by selective contact diffusion

Devices were fabricated in MBE (molecular-beam epitaxy)-grown wafers with a ten period doping superlattice consisting of 300-Å layers with n=p=3×10¹⁸ cm^-3, using sequential patterned sulfur and zinc diffusions. The typical contact spacing was 5 μm, and the devices were generally 400 μm long. Excellent I-V characteristics were achieved with reverse breakdown voltages in excess of 9.5 V, indicating that the selective contacts were nearly optimum. CW outputs of 500 μW at 50-mA drive current have been observed from the surface of the devices at room temperature. Measurements of the current-voltage characteristics and electroluminescence spectra have been performed from 3 to 300 K. The LED output spectrum tuned at a rate of about 700 meV/V of applied bias at 120 K. Good correlation was observed between the forward characteristics of the diodes and the tuning of the electroluminescence. The tunneling component of the diode current has been identified and remains significant to temperatures of ≈140 K. As the tunneling component is reduced, the tunable luminescence is quenched due to the competition from thermally injected carriers recombining across the bandgap