New Local Vibrational Modes Related to Silicon in Bulk AlGaAs

Abstract

A silicon-related local vibrational mode absorption in AlGaAs is reported for the first time. It consists of six peaks grouped around 450 cm -1 which form a distinct pattern. We believe tlat the new local vibrational mode absorption is a fingerprint of a single defect. Among the discussed microscopic structures the most plausible is a SiG a -SiA S pair complex with Silks acceptor interacting with different Ga, Al nearest neighbour local environments.PACS numbers: 61.72. Vv, 63.20.Pw, 71.55.Eq A cucial factor limiting the sensitivity of local vibrational mode spectroscopy of ternary alloys is the sample thickness. With nonequilibrium growth techniques like MBE or MOCVD (metalorganic chemical vapour deposition) one is able to grow layers of up to 10 μm only. In this case a high doping density is required leading inevitably to creation of complexes and precipitates. Our LPEE (liquid phase electroepitaxy) grown thick (up to 400 μm) AlGaAs samples with very high compositional uniformity (±1%) and relatively low doping levels (5 x 10 17 cm-3) are a worldwide unique high quality material for studying local vibrational mode absorption of isolated defects and simple complexes in ternary compounds.In our experiment silicon, as a light impurity, has been introduced into the AlGaAs matrix. Although the Si impurity was thorouglly investigated in GaAs l ,. means of the LVM (local vibrational mode) technique (for review see e.g. [1]) there is little known about its behaviour in alloys. Additionally, Si is interesting from the point of view of its DX behaviour related to the localized vibrations. This problem is still under dispute [1]. In the alloy, the solution of this issue can be attempted without using highly sophisticated equipment needed for high pressure experiments [2].Our Alx Ga1-x As:Si samples were grown by the liquid phase electroepitaxy method [3] with two different alloy compositions: x = 0.25 (direct band-gap) and 0.43 (indirect band-gap). The doping levels and sample thicknesses were 1.5 x 10 18 cm-3, 360-400 μm and 5 x 10 17 cm-3 , 150 μm, respectively. The control (75i91

Magneto-optical and magnetic resonance investigations of DX centres in Te-doped

“…The absorption cannot be due to a transition to either the valence band or the nearest conduction band for energetical reasons. It is thought that it is a transition to the X 3 -band minimum, in agreement with Kaczor et al (1993) and our previous results on Si. Note, that a very similar MCDA has been observed previously for shallow Te 0 and S 0 donors in GaP, which was interpreted as a transition to the L-band minimum (Spaeth et al 1993) (see figure 7(b) for comparison).…”

“…The failure to see the MCDA in an LPE sample with x = 0.35 (Peale et al 1991) seems consistent with the failure to see the IR band above 0.5 eV for x = 0.37 reported by Mori et al (1992). However, Kaczor et al (1993) reported an IR band peaking at 0.53 eV for x = 0.3 in a sample also grown by the LPE method, but apparently from a different crystal grower. It is not clear why this IR band was not observed either by Peake et al (1991) or by Mori et al (1992) for a similar Al content.…”

“…For Si 0 it was found that the onset of the MCDA (and of the maxima) shifts to higher energy with increasing Al content. Such a trend was also observed by Kaczor et al (1993) . They show the same trend with the Al content following the X-band minimum.…”

“…Later magnetooptical measurements on a substrate-free Te-doped sample with x = 0.35 failed to detect this paramagnetic state (Peale et al 1991). On the other hand, Mori et al (1992) and Kaczor et al (1993) have measured infrared absorption bands which appear after photoionization of DX centres peaking at about 0.6 eV, which were associated with the metastable Te 0 donors. It was the purpose of this work to investigate Te-doped Al x Ga 1−x As, which showed the photoinduced infrared absorption bands ascribed to Te 0 donors, using magnetooptical methods in order to see whether these bands belong indeed to a paramagnetic ground state and whether they can be correlated with the EPR spectrum found previously.…”