Far-infrared photoconductivity spectroscopy of high-mobility n-GaAs grown by MBE

Abstract

n-GaAs of high peak mobility (p=250 000 cm2 V-' S-' ) has been grown in a molecular beam epitaxy (MBE) system with modified source-furnace geometry. High-resolution far-infrared magnetospectroscopy has been performed on this material. The photoconductive response at 2-4 K reveals a rich spectrum of excited state transitions. These are identified from theoretical models, and transitions from the ground impurity state up to the N=8 Landau level are noted. For the first time in MBE material, transitions involving D-states are observed.

Studies of far-infrared magneto-photoconductivity of D− centers in GaAs/AlxGa1−xAs multiple quantum wells

“…However, this picture cannot explain our experimental results completely. First, the increased binding energy calculated from the model is on the order of several tenth cm 21 which is not comparable with our measured 3.5 cm 21 . In addition, this picture cannot explain the peculiar change (an initial increase then a decrease) of the D 2 center binding energy in the experiments.…”

“…The former peak was reported as the 1s±2p 1 transition of the residual donor impurities in the bulk GaAs substrate under similar conditions [20]. The 3.23 T peak also comes from the donor impurity transition of the bulk substrate but is related to the metastable state [21,22], i.e. a state that arises in a magnetic ®eld out of the donor continuum and does not lead to a donor bound state in the zero ®eld limit.…”

Excited-state spectroscopy of confined shallow donor impurities in a multi-quantum well

“…The behaviour of the ls-2p+ peak noted in figure 3 is consistent with previously reported experimental measurements for similar wells [2, 31 and with theory [l]. Figure 3 also displays equivalent data for bulk GaAs [7], the systematics of which are markedly different to the high-energy features noted here. The ls-2p+ peak in figure 1 is due to impurities at the centre of the well: any possible redistribution of these impurities would produce spectral features at higher magnetic field (lower energy).…”

“…The assignments of the MQW spectral features plotted in figure 3 are listed in table 1, together with assignments of n-GaAs bulk material given by Grimes et aI [7]. The ordering of the transitions is assumed to be the same for both cases and it is noteworthy that the relative sizes of the photoresponse for various spectral lines is often similar for both MQW and bulk samples.…”

Central-cell corrections for Si and S in GaAs in a strong magnetic field

“…Zero-field central-cell corrections have been extensively studied with a view to identifying the different chemical species involved. [8][9][10][11][12][13][14] Compared to this large amount of work on the zero-field case, the magnetic-field dependence of the centralcell correction has been subject to little study. An early report gave the difference in chemical shift for two unidentified donors.…”