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Proceedings Paper

Characterization of InGaAs strained layers on GaAs: comparison of dislocation densities with device performance
Author(s): John F. Walker; J. M. Bonar; Robert Hull; Roger J. Malik; R. W. Ryan
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Paper Abstract

We present a study of the electrical and structural properties of 1atUcemismatched InGa,.As strained layers grown on GaAs (100). This strained system has been used in device structures because of the high carrier mobilities which may be obtained, but the inherent misfit strain is known to produce dislocations above some critical limit. We have grown, by molecular beam epitaxy (MBE), structures with p-type (Be), 8 x1019 InGa,As layers of 20 nm thickness. The indium mole fraction, x, was increased in subsequent samples from 0 to 0.50 in steps of 0.05, simulating the base of a heterojunction bipolar transistor (HBT). We correlate hole mobilities and sheet resistances with the microstructure of the strained layers as determined by transmission electron microscopy (TEM). It is shown that the hole mobility drops from 55.3 cm2V-'s-' to 31.7 cm2V-1s-1 x varies from 0 to 0.50, with a corresponding rise in sheet resistance. For x □0.40, significant reduction in electrically active carrier concentrations is observed, presumably due to interaction with the extensive defect structure. HBT structures incorporating the base layers described were grown by MBE and processed into devices. These devices show a maximum gain at x= 0.10, with good I-V characteristics, and a subsequent sharp fall in gain at higher x, with consequently poorer I-V characteristics. We believe this shows a higher sensitivity of minority carriers to the dislocation network than majority carriers. No misfit dislocations are visible in plan-view ThM until x= 0.25-0.30, considerably higher than the Matthews-Blakeslee mechanical equilibrium prediction of x= 0.10. This confirms the relatively sluggish relaxation of these structures at the growth temperature of 500°C. Further, we demonstrite that for x□0.4, generation of new misfit dislocation length is not by deflection of pre-existing threading dislocations, but rather by generation of new misfit dislocation ioops.

Paper Details

Date Published: 1 October 1990
PDF: 10 pages
Proc. SPIE 1285, Growth of Semiconductor Structures and High-Tc Thin Films on Semiconductors, (1 October 1990); doi: 10.1117/12.20814
Show Author Affiliations
John F. Walker, Lab. TASC (Italy)
J. M. Bonar, AT&T Bell Labs. (United States)
Robert Hull, AT&T Bell Labs. (United States)
Roger J. Malik, AT&T Bell Labs. (United States)
R. W. Ryan, AT&T Bell Labs. (United States)

Published in SPIE Proceedings Vol. 1285:
Growth of Semiconductor Structures and High-Tc Thin Films on Semiconductors
Anupam Madhukar, Editor(s)

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