The control and modeling of doping profiles and transients in MOVPE growth

The redistribution of Zn in the base region of GaAs‐AlGaAs heterojunction bipolar transistor structures during growth by organometallic vapor phase epitaxy has been examined with respect to the presence of Si doping in the emitter‐contact, emitter, and collector/subcollector layers, and as a function of Zn doping concentration and Si counterdoping level in the p+ base. For a growth temperature of 675 °C the Zn shows no significant redistribution up to concentrations of 3×1019 cm−3 without Si doping. The addition of Si to the adjacent AlGaAs emitter and collector/subcollector layers causes substantial diffusion of Zn from the base, while Si doping of the GaAs emitter contact results in even greater Zn redistribution. Under these conditions, the Zn concentration in the base attains a maximum value of ∼7×1018 cm−3. Silicon counterdoping in the base region retards the Zn diffusion, while strain introduced by an InGaAs cap layer has no effect on the Zn redistribution.

Redistribution of Zn in GaAs-AlGaAs heterojunction bipolar transistor structures

We report a comprehensive optical wafer evaluation technique for C-doped n-p-n heterojunction bipolar transistors (HBT) using low temperature photoluminescence spectroscopy. The correspondence between the optically determined parameters at the wafer level and the electrical device parameters is demonstrated. The hole density in the base of transistor structures was obtained from optical transitions in the p/sup +/-GaAs layer exploiting the bandgap narrowing effect. Furthermore, our experimental studies, which combine optical and electrical measurements, show that a photovoltaic effect observed in the optical spectrum measures the strength of carrier recombination processes in the emitter-base heterojunction region. Because interface recombination strongly affects the dc current gain of these devices, photoluminescence spectroscopy of epitaxial wafers provides critical information on HBT device parameters prior to device fabrication.

A comprehensive optical characterization method for high-performance n-p-n AlGaAs-GaAs heterojunction bipolar transistors

GaAs bipolar transistors of different emitter types have been fabricated from MOCVD grown lattice matched Ga0.5In0.5 P/GaAs layer structures using carbon for heavy base doping (p=2×1019 cm-3). Besides conventional heterojunction bipolar transistors we also investigated tunneling emitter bipolar transistors having 2 and 5 nm thin GalnP layers between emitter and base, which act as a hole repelling potential barrier in the valence band. Current gains up to 115 have been obtained at collector current densities of 104 A/cm2 even for this heavy base doping. All devices show an almost ideal output characteristics with large Early voltage and small offset voltage. From the temperature dependence of the collector current a small effective conduction band barrier at the heterointerface is determined which hardly affects electron injection into the base.

A Novel GaAs Bipolar Transistor Structure with GaInP-Hole Injection Blocking Barrier

Electrical transport measurements are very sensitive to the structure of a heterojunction This sensitivity is used in conjunction with a realistic model for the band diagram to determine the position of the dopant junction relative to the metallurgical junction This electrical technique involves the determination of an effective barrier height from temperature‐dependent I‐V measurements and comparison with calculated barrier heights The sensitivity of the electrical characteristics to the device structure can often be greater than that of secondary ion mass spectroscopy or C‐V profiling GaAs/Al030Ga070 As p+‐n heterojunctions grown under a variety of conditions are used to demonstrate this technique Growth conditions which produce abrupt zinc profiles are discussed

H. Baratte

Papers

The influence of growth conditions on the electrical properties of GaAs/Al0.30Ga0.70As p+/n heterojunctions

Electrical characterization of GaAs/Al0.30Ga0.70 As p+‐n heterojunctions grown by metalorganic vapor phase epitaxy