Charge Density Profiles of Close Spaced Vapor Transport GaAs Epitaxial Layers

Abstract

normalGaAs epitaxial films have been deposited on heavily Si‐doped (100) normalGaAs substrates by closely spaced vapor transport from a semi‐insulating (undoped) normalGaAs source. Charge density (N) profiles of the epitaxies have been determined electrochemically by a succession of photocorrosion steps and capacitance measurements. When the films are thick enough, typicalN profiles show four regions. Starting from the surface of the film and going toward the normalGaAs substrate, there is a first region (I) of constant N, extending over a length varying with the deposition time. It is followed by a second region (II) extending over 12±2 μnormalm , where N slowly rises. In region III , there is an abrupt increase of N followed by region IV which is the substrate region. Consistently, close spaced vapor transport technique layers were n‐type with N values in region I varying from 4×1015 normalto 2×1016 cm−3 . Region III of the N profile displays a fine structure which has been explained in terms of Si which is released from the Si‐doped normalGaAs substrate into the vapor phase and redeposited within the growing film. Region III is also due to Si diffusion from the substrate into the growing film. A diffusion coefficient of Si into normalGaAs of 6.5±2.5×10−14 cm2 s−1 at 760°±3°C has been calculated from the N profile curves. The slow variation of N in region II results neither from a fast diffusive shallow donor impurity from the normalGaAs substrate, nor from Si released from region III into the vapor phase and redeposited into the growing film. It is suggested that region II probably reflects a variation of the off‐stoichiometry in the epitaxial film. Epitaxial layers of normalGaAs grown on semi‐insulating (SI) (100) normalGaAs substrates show region I and II of the N profile curve. Hall effect measurements performed on these layers agree with the electrochemical results.

Growth by the CSVT (close-spaced vapor transport) technique and characterization of epitaxial GaAs layers on Ge substrates

“…Our experience with CSVT has been to grow GaAs epitaxial layers from various kinds of sources (undoped semi-insulating (14), n type (6), and p type GaAs (7)) to control the electrical properties of the layers. All these films were obtained on GaAs substrates of about 1 cm'.…”

Electrical Characterization of GaAs Epitaxial Layers Grown by CSVT from Zn‐doped GaAs Sources

“…This was already observed for layers grown from SI GaAs sources on Si-doped or Si GaAs substrates. It was shown not to be related to the diffusion of a n-type impurity from the substrate (11). It seems however to be affected by the temperature rise conditions and is presently under study.…”

“…1, VFB is ~ --2.0 or ~ -0.5 V for n-type or p-type GaAs, respectively. Since the resolution of the electrochemical profilometry technique has been found to be ~ 0.1 ~m (11), it indicates that the change from p-to n-type character of these films extends from 1 to 2 ~m. The doping of the n-type layer is inhomogeneous in the growth direction.…”

“…Figure 3 also presents the mobilities of films already obtained by CSVT with SI GaAs sources (10,11). Full squares are the mobilities measured with our present control of the background doping which is in the low 10 TM cm "~ range (11).…”

“…CSVT system and epitaxy conditions.--The close-spaced system and deposition procedure have already been described (11). All films were grown using the following deposition parameters: source temperature, T'I = 800~ substrate temperature after equilibrium, T'2 = 760~ distance between the surface of the source and the surface of the substrate, ~ = 0.03cm; water vapor pressure, PH2O = 4.58 Torr (unless otherwise mentioned).…”