EFFECT OF DOPING ON THE RELIABILITY OF GAAS MULTIPLE-QUANTUM-WELL AVALANCHE PHOTODIODES

The effect of various doping methods reliability of gallium arsenide/a luminum gallium (GaAs/AlGaAs) multiple quantum well (MQW) avalanche ph otodiode (APD) structures fabricated by molecular beam epitaxy is inve stigated, Reliability is examined by accelerated life tests by monitor ing dark current and breakdown voltage, Median device lifetime and the activation energy of the degradation mechanism are computed for undop ed, doped-barrier, and doped-well APD structures, Lifetimes for each d evice structure are examined via a statistically designed experiment, Analysis of variance (ANOVA) shows that dark current is affected prima rily by device diameter, temperature and stressing time, and breakdown voltage depends on the diameter, stressing time, and APD type, It is concluded that the undoped APD has the highest reliability, followed b y the doped-well and doped-barrier devices, respectively, To determine the source of the degradation mechanism for each device structure, fa ilure analysis using the electron-beam induced current method is perfo rmed. This analysis reveals some degree of device degradation caused b y ionic impurities in the passivation layer, and energy-dispersive spe ctrometry subsequently verifies the presence of ionic sodium as the pr imary contaminant. However, since all device structures are similarly passivated, sodium contamination alone does not account for the observ ed variation between the differently doped APD's, This effect is expla ined by dopant migration during stressing, which is verified by free c arrier concentration measurements using the capacitance-voltage (C-V) technique.