Deep electron traps have been studied by means of deep level transient spectroscopy in n-type nominally undoped and intentionally Te-doped AlxGa1−xAs epitaxial layers which were grown by vapor phase epitaxy from organometallic compounds (OMVPE). Three main deep electron levels are present in undoped material: a trap with an activation energy of 0.8 eV, which is also found in GaAs grown by conventional VPE, and two levels specific to OMVPE with activation energies of 0.32 and 0.38 eV, respectively. The concentration of the 0.8 eV level is found to be independent of the aluminum content x, supporting the assumption that it is not related to substitutional oxygen. The other levels, however, exhibit a very strong dependence of concentration on the composition, varying by four orders of magnitude in the range of 0⩽x⩽0.35. In Te-doped samples, a level with an activation energy of 0.23 eV has been identified, which is thought to be related to an IR emission found in photoluminescence in OMVPE as well as in liquid phase epitaxial material.
A modification of the cold-wall organometallic vapor-phase epitaxial (OMVPE) process for the growth of AlxGa1−xAs layers is described. Graphite baffles placed in the gas stream act to greatly increase the photoluminescence efficiency of the AlxGa1−xAs. Preliminary evidence indicates that the effect of the baffles may be to provide a solid surface upon which Al2O3 can be deposited from the reaction of trimethylaluminum with any residual O2 and/or H2O in the vapor phase. The ’’gettering’’ action apparently reduces oxygen contamination of the AlxGa1−xAs.
Es wird gezeigt, daß epitaktische GaAs‐ Schichten zur Herstellung von Oberflächenbarriere‐Feldeffekttransistoren mit Hilfe des Systems AsH3 + HCl + Ga + H, aus der Gasphase abgeschieden werden können.
Epitaxial layers of GaAs suitable for fabrication of MESFET devices have been grown by the hydride VPE technique (ASH3 + HC1 + Ga + H2). The materials properties and FET characteristics of devices fabricated in this material are similar to those for LPE, and the more common AsCls VPE growth techniques. The uniformity of sheet resistance of this material over a substrate area of --~6.5 cm2 is typically ,~5% (standard deviation from the mean). A new technique has been developed for the growth of buffer layers. The background doping level of 4-9 X 1013 cm -8 is found to be reduced to <1014 cm -~ by the addition of NH3 to the AsHs stream. More complex n+/n/ buffer layer structures have been grown in a single operation by simply programming gas flow rates during the run. * Electrochemical Society Active Member.
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