The ordered–disordered transition in Si delta-doped GaAs

Abstract

We report results for Si layers embedded in GaAs, extending from the delta-doped (δ-doped) range up to 6 monolayers (MLs) derived by means of variable temperature resistivity and Hall effect measurements, secondary ion mass spectrometry (SIMS), and high resolution x-ray diffractometry (HRXRD) techniques. The conductivity transition from free carrier transport in ordered δ-layers (<1 ML) to strongly localized two-dimensional variable range hopping (2D-VRH) transport under potential fluctuation disordered conditions (≳4 ML) is clearly observed. This observation is in good agreement with the SIMS and HRXRD data. Results from the intermediate case with 2–3 MLs are also discussed.

Electrical conduction properties of Si δ-doped GaAs grown by MBE

“…In this work, the obtained carrier density and mobility are the same magnitude as reported earlier for this system [10,15,16]. Hai et al [16,17] .…”

“…Then, it is possible that the hopping regime can be observed in a wide temperature range. In Si d-doped GaAs, presence of residual acceptors can create vacant positions in the impurity band and this results in a 2D variable-range hopping (VRH) conduction in the d-plane [10]. The vacancy defect is identified as the Ga vacancy in the Si d-doped GaAs.…”

“…Past studies for the transport properties of d-doped layer indicates that the conductivity in the d-doped layer is of ''hopping'' type like when nffi10 9 -10 12 cm À2 , it is ''metallic'' type like when nffi10 14 cm À2 [5,10,12,13]. However, several works show that it is possible to observe 2D VRH in d-doped layer even if it is degenerate [10]. Although, the Si d-doped GaAs samples having 4 and 6 monolayers of Si d-doped layer (nffi10 11 -10 13 cm À2 ) were degenerate, 2D VRH conduction was observed [10].…”

“…However, several works show that it is possible to observe 2D VRH in d-doped layer even if it is degenerate [10]. Although, the Si d-doped GaAs samples having 4 and 6 monolayers of Si d-doped layer (nffi10 11 -10 13 cm À2 ) were degenerate, 2D VRH conduction was observed [10]. Khondaker et al [13] reported that the 2D VRH conduction appears in a disordered 2D electron gas in d-doped GaAs/AlGaAs heterostructure with values of n ¼ 0.91-1.85 Â 10 11 cm À2 .…”

Evolution of Si-on-GaAs (001) surface morphology towards self-organized ordered Si structures

“…[6][7][8][9] In Si adsorption experiments carried out on c͑4ϫ4͒ reconstructed surfaces, 10 ''needle-like'' islands were found to form by Si-As dimer exchange with the additional outermost arsenic layer. Other studies show that Si preferentially occupies the vacant second layer Ga sites in the missing dimer trenches of the ͑2ϫ4͒␤2 reconstructed surface.…”