The III-V semiconductor 1.06 micrometers electro-optic structures

The most significant results to date have been concentrated in the material and device development area. In the material area, three alloys systems have been explored, GaAsSb, GaAlSb, and InGaAsP. The high dislocation density of GaAsSb has been reduced by a series of lattice matching layers. An intensive study of dopants in this material has been made and doping control to the low 10 to the 15th power per cu cm has been achieved. A doping drop method has been developed to reduce interface defects and compositional variation in the grown layer. In the GaAlSb system the better lattice match between epilayer and substrate results in a very smooth surface morphology. Avalanche photodiodes fabricated from this system show extremely uniform photoresponse over the entire optically active area even at microwave avalanche gains as high as 20. A detailed study of the electron and hole ionization coefficients have been made and indicate a factor of two difference. This implies an excess multiplication noise factor of 0.75 which, although larger than the silicon (0.4), is significantly smaller than GaAs (1.0). The most promising material system is the InGaAsP quaternary. In this system, the epilayer lattice constant is 'forced' to match that of the substrate. The best surfaces of any III-V system have been achieved in the quaternary. LEDs fabricated from grown layers show excellent performance, and lifetime tests are currently being initiated.