Thermal and bias stabilities of InP/InGaAs composite-collector DHBT

This study proposes composite-collector double heterojunction bipolar transistors (CC-DHBTs) made by low-pressure metamorphic organic chemical vapor deposition (LP-MOCVD). Both V-shaped behaviors (observed in dc current gain, beta, against collector current, I_C, and in offset voltage, V_CE,offset, against base current, I_B, plot) of the asymmetric CC-DHBT are studied. At high I_C, the presented CC-DHBTs improve the dc current gain temperature stability relative to most HBTs described in the literature. Additionally, unlike that of the abrupt DHBTs in the literature, the beta of the CC-DHBTs is independent of V_CB, suggesting that the effect of the conduction-band barrier in the base-collector junctions may haven been eliminated. An analytical expression for the variation of V_CE,offset with I_B has been developed. Additionally, unlike that of the unpassivated and SiN_x-passivated devices, the beta of the sulfur-treated device is fairly constant over five decades of I_C. The difference betreen these variously treated devices is remarkable. X-ray photoelectron spectroscopy was applied to study InGaAs surfaces that were (NH₄)₂S_x and SiN_x passivated. The results demonstrate that passivation effectively suppresses the oxidation of As.