High performance 1300 nm photodetectors grown by molecular beam epitaxy
Photodetectors operating at 1.3 µm on GaAs substrates with low noise, low dark current, high quantum efficiency and high bandwidth are very attractive for applications in long haul, fiber optic communication systems. GaAsSb is a promising material for 1.3 µm emission and absorption on GaAs substrates. However, GaAsSb is not lattice-matched on GaAs substrate and As and Sb have different sticking coefficients with Ga, which makes both the growth and device realization difficult. This dissertation discusses the molecular beam epitaxy (MBE) growth of compressively strained GaAsSb layers on GaAs substrates. We found that the optical properties and alloy composition of GaAsSb highly depend on the growth parameters, such as growth temperature, Ga growth rate, Sb and As fluxes. We also reported two resonant-cavity-enhanced (RCE) avalanche photodiode (APD) structures with GaAsSb/GaAs multiple quantum well absorption regions. The RCE GaAsSb p-i-n photodiode exhibited a peak external quantum efficiency of 54% at the wavelength of 1.3 µm with a full-width-at-halfmaximum of 8 nm. In the RCE GaAsSb APD with separate absorption, charge and multiplication regions (SACM), the high electric field multiplication region was separated from the intrinsic absorption region. As a result, the RCE GaAsSb SACM APD exhibited very low dark current (~5 nA) at 90% of the breakdown. By utilizing thin undoped Al0.9Ga0.1As layer as the multiplication region, very low multiplication noise with k value ~ 0.1 was obtained in the SACM APD. This is the lowest noise reported to date for APDs operating at 1.3 µm.