Studying the Effect of Electrically Active Impurities Coming from Trimethylgallium Synthesized by Different Means on the Electrophysical Characteristics of Gallium Arsenide Epitaxial Layers

Abstract

Chemical deposition from vapors of metalorganic compounds and volatile hydrides (metalorganic vapor phase epitaxy) is the main way of growing devices’ heteroepitaxial structures based on gallium arsenide (GaAs) and solid solutions of it (Al_xGa_{1 – x}As and In_yGa_1 – yAs) on an industrial scale. Electrically active impurities deposited uncontrollably on epitaxial layers during growth worsen the electrophysical parameters of devices’ structures. Sources of deposited background impurities include the initial material. In this work, ways of synthesizing trimethylgallium (TMG) are compared from the viewpoint of impurities, especially electrically active GaAs, being incorporated into the final product. Ways of preparing TMG that include the exchange reaction between gallium trichloride and trimethylaluminum (TMA) and magnesium–organic syntheses in which metallic magnesium is used as the initial reagent are selected as the objects of study. The behavior of electrically active impurities during the purification of TMG via rectification is studied. The investigations are performed by means of spectral analysis and functional control over the growth of electrophysical parameters of GaAs epitaxial layers from TMG and arsine. It is established that the qualitative and quantitative composition of impurities in TMG depends on their content in the initial reagents. TMG prepared using the exchange reaction between gallium trichloride and TMA is the source of n-type impurities in GaAs. These are mainly Group IV elements (silicon, tin, and lead), with silicon impurities predominating. TMG fabricated using metallic magnesium is a source of both p- (preferentially zinc) and n-type (preferentially silicon) impurities. Irrespective of the quality of the initial raw TMG, the use of reduced-pressure rectification allows the fabrication of TMG with low impurity contents. Epitaxial GaAs layers grown using purified TMG (TMG rectificate) have n-type conduction with a low level of background doping (0.7–4) × 10¹⁴ cm^–3 and high carrier mobilities of 7300–8500 cm²/(V s) at 300 K and 90 000–156 000 cm²/(V s) at 77 K. These values correspond to purest samples made with TMG and arsine using MOC-hydride epitaxy. Based on the data on functional control, the content of impurities that display electrical activity in GaAs is on the level of 10⁻⁷–10⁻⁶ at % in fabricated TMG-rectificate samples.