PRODUCTS OF THERMAL-DECOMPOSITION OF TRIETHYLGALLIUM AND TRIMETHYLGALLIUM ADSORBED ON GA-STABILIZED GAAS(100)

We report mass spectrometric studies of the products of thermal decomposition of triethylgallium (TEGa), and trimethylgallium (TMGa) adsorbed on Ga-stabilized GaAs(100) in ultrahigh vacuum. Adsorbed layers were prepared by dosing clean GaAs, near room temperature, to either saturated coverage or coverages below saturation. Subsequent heating leads to desorption of products, detected by a differentially pumped quadrupole mass spectrometer. Total carbon coverage was monitored by X-ray photoelectron spectroscopy (XPS). The substrate temperature was measured by infrared laser interferometric thermometry. At saturated coverage, TEGa decomposes upon heating (1-2°C/s) to yield one third Ga-alkyl product (Ga(C2H5)2) between 0 and 300°C, and two thirds hydrocarbon products (mostly C2H4 and some C2H5) between 250 and 390°C. About 25% of the Ga deposited from TEGa remains on the surface after all products desorb. Below 40% of saturated coverage, only the higher temperature hydrocarbon products desorb, and all adsorbed Ga remains on the surface. TMGa behaves similarly; starting at saturated coverage, Ga-alkyl product (either Ga(CH3)2 or a mixture of Ga(CH3)2 and TMGa) desorbs at low temperature (50-380°C) and hydrocarbon product (CH3) desorbs at higher temperature (250-425°C). However, for TMGa the yield of the Ga-alkyl is about twice the CH3 yield. No ethane, or butane was detected in TEGa decomposition, nor was any ethane found for TMGa decomposition, indicating that association and disproportionation reactions are unimportant. Also no As-alkyl products were detected. The slower rate of desorption of CH3 for TMGa decomposition, compared to C2H4 and C2H5 desorption from TEGa decomposition, qualitatively explains higher carbon levels in GaAs films grown with TMGa versus TEGa. © 1990.