Characterization of Oxygen and Carbon in Undoped AlGaAs Grown by Organometallic Vapor-Phase Epitaxy

Abstract

We have systematically characterized oxygen (O) and carbon (C) impurities in undoped gallium aluminum arsenide ( Al x Ga1- x As) epitaxial layers grown by organometallic vapor-phase epitaxy (OMVPE). The concentrations of O and C impurities are evaluated by secondary-ion mass spectroscopy. For x≤0.63 the increase rate of O concentration, [O], with x is nearly proportional to the flow rate of trimethylaluminum (TMA), indicating that the oxygen is contained in the TMA molecules. In contrast, [O] and [C] increase superlinearly with x for x≥0.83, and particularly, [O] exceeds 1018 cm-3. The vibration mode of Al–O bonds is observed at 900–1050 cm-1 for the x=0.83 sample using Fourier-transformation infrared measurements. The superlinear increase of [O] with x is attributed to the increased adsorption of residual O2 or H2O molecules. The mechanism of the superlinear increase is discussed in terms of statistic consideration of the –Al– arrangement on the Al x Ga1- x As surface. Hall measurements show that the hole concentration markedly decreases for x>0.63 and the Al x Ga1- x As layer becomes semi-insulating, which was attributed to hole compensation by the O-related deep hole traps. The hole mobility also decreases in the same x range.

Influence of growth parameters on the composition and impurity levels of intrinsically carbon doped AlxGa1−xAs

“…The incorporation of aluminum gives rise to the presence of oxygen in the lattice, which is in accordance with literature [12,17,26]. At reduced T G and V/III ratio, however, there is a considerable oxygen level even at a low aluminum fraction, which was also found by Fujii et al [18].…”

“…In contrast, the concentrations of carbon show a super-linear dependence on x for samples grown at standard growth conditions. In the literature, the relation between the carbon (or hole) concentration and aluminum fraction has been reported to be linear [11,20] as well as superlinear [16,17]. Careful examination of the literature shows that linear dependencies were reported for growth conditions that induce high carbon levels, whereas super-linear trends were solely obtained at growth temperatures X650 1C and high V/III ratios.…”

“…In most of these studies carbon is regarded as an unintentional contamination occurring at the generally applied growth conditions, i.e. temperatures above 600 1C and V/III ratios 410 [16][17][18][19]. Recently, the incorporation of carbon in Al x Ga 1Àx As was revisited as a research topic [11].…”

Parameter study of intrinsic carbon doping of AlxGa1−xAs by MOCVD

“…However, there has been some controversy about the quantitative relation between doping level and aluminum fraction (x) in the Al x Ga 1Àx As layer. The studies concerning unintentional carbon incorporation report a super linear [37] or, more precisely, a squared relationship [31,36] between doping level and x. Others reported a strong increase of carbon up to an x of 0.5-0.7 and approximately constant for higher x [15,38].…”

Design and Realization of Novel GaAs Based Laser Concepts

“…Additionally, aluminum has a strong intrinsic affinity to oxygen, which makes it very sensitive for precursor impurities. Thus, the use of AsH 3 with non-optimal quality can lead to increased oxygen incorporation, depending on the V/III ratio [Kak96], whereas TBAs-based growth shows a V/III ratio that is almost independent of oxygen concentration [Leu98]. Different growth conditions for Al 0.8 Ga 0.2 As layers employing TBAs and AsH 3 were investigated by Hall measurements and are summarized in Table 4.2.…”