Auger Recombination and Impact Ionization in Semiconductor Lasers and Avalanche Photodiodes.

The telecommunication industry has been advancing very fast. Having used.8 μm optical fiber systems for a short time, the industry has quickly shifted to 1.3 and 1.5 μm optical fiber communication systems to achieve lower loss and longer distance between repeaters. However, the performance of the transmitters and receivers in the current long wavelength communication systems is not able to match that in the 0.8 μm communication system. The most serious problem with InGaAsP/InP lasers for 1.3 and 1.5 μm communications is their poor temperature performance. The threshold current of these lasers increases drastically with temperature at room temperature. This either causes thermal-run-off or makes a thermal controller a necessity even for a low -power laser. Studies have shown that the poor temperature performance in InGaAsP/InP lasers is caused by Auger recombination carrier losses. In GaAs lasers, Auger recombination carrier loss is not severe enough to degrade performance. However, it has been the major problem for most long-wavelength semiconductor lasers, such as InGaAsP/InP lasers for 1.3 and 1.5 μm communications. Not only transmitters, but also receivers for 1.3 and 1.5 μm communications face similar challenge. The performance of the InGaAsP/InP avalanche photodiodes (APDs) used in current systems is far from that of the Si APDs, which are nearly perfect, used in 0.8 μm systems. Avalanche (impact ionization) processes are the reverse Auger processes --carrier creation processes. They provide current amplification. Because virtually only one type of carrier (electron) multiplies in Si, the APDs have low noise figure and high gain-bandwidth products. The electron and hole impact ionization rates in InP are alike, which means the multiplication is a delayed positive feedback process. Therefore, these APDs are noisy amplifiers and have low gain-bandwidth products. At the best operating condition, the gain for a Si APD of several hundreds is typical, whereas for a InGaAsP/InP APD, the gain is 10-50. These deficiencies in the transmitters and receivers for long-wavelength communications challenge us to investigate new materials and structures. AlGaSb APDs have shown low noise and high gain-bandwidth product. GaSb quantum well laser and InGaSb strained quantum well laser are proposed to have improved performance over InGaAsP/InP laser. HgCdTe/CdTe multi-quantum well (MQW) and quantum box (QB) laser are very promising for application in the 2-5 mu m wavelength range. This work studies these materials and structures.