Identification of Residual Impurities in Si-Doped MBE Grown GaAs

Abstract

The changes of dopant vaporizatioii enthalpy in GaAs:Si grown by molecular beam epitaxy revealed the presence of residual donors related to group VI elements. This has been confirmed by deep level transient spectroscopy studies of AlGaAs:Si layers grown in the same MBE system. It is argued that a commonly observed deep trap labelled E2 is probably related to Te, Se or S. The measurements have been performed oii near-ideal Al Schottky barriers grown in situ by MBE. PACS numbers: 73.40.Νs, 71.55.Eq, 73.20.Hb It is generally accepted that Si is an almost ideal dopant for n-type GaAs grown by molecular beam epitaxy (MBE). At present the layer doping is still largely empirical and often, at low doping levels residual impurities disturb calculated dependences. Usually shallow acception can be readily identified by low temperature photoluminescence measurements. The chemical identities of shallow donors are more difficult to determine by simple methods, and resort has to be made to far-infrared photothermal ionization or very high resolution Zeeman photoluminescence studies.In this paper we discuss an unintentional codoping process during the growth of GaAs:Si by MBE. Thick epitaxial layers of GaAs were grown at 580°C on semi-insulating (001) oriented GaAs using the Riber 32Ρ MBE system, which has a background pressure < 1 x 10 -I 0 torr. High purity Ga (7Ν), As (7Ν) and Si (< 1012 cm-3 intrinsic) source materials were used. To achieve a full range of Si concentration the temperature of Si effusion cell was changed from 550°C to 1130°C, whereas those of Ga and As were held constant at 945°C and 2180C, respectively. The beam equivalent pressure As/Ga ratio was equal to 9.5. All layers were grown at constant rate 1 μm/h. Electrical properties of the epitaxial layers were characterised by Van der Pauw measurements. The effects of surface and (775)

Mobility spectrum approach in the analysis of the electrical conduction of a GaAs layer grown by molecular beam epitaxy

“…So far, we do not know which element it is. The observed value of vaporization enthalpy, Ϫ1.1 eV, and deep level transient spectroscopy ͑DLTS͒ experiments performed on AlGaAs samples made in the same machine 6 show that the residual dopant is an element from group VI ͑S, Se, and Te͒. Our results show that only those elements which are able to diffuse from the Si-doped epilayer to the buffer can be responsible for LMC conduction.…”

“…It was proved, in the case of our MBE machine, that during the Si doping some additional donors from group VI elements are unintentionally introduced into the GaAs layer. 6 Their presence is usually masked by Si donors for temperature of an Si effusion cell above 900°C. However, below this temperature the group VI dopants exceed the intentional Si doping level.…”