Irradiation-Induced Damage and Intermixing of GaAs-Algaas Quantum Wells
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samples were masked during irradiation for direct comparison with unirradiated material. The irradiation doses vary from 1 x 1012 cm-2 to 4.3 x 1016 cm-2. After irradiation, the samples (both irradiated and unirradiated regions) were annealed face down on a fresh piece of GaAs (to prevent excessive loss of As from the surface) in a rapid thermal annealer (RTA) at 900 'C for 30 s. Low temperature (12 K) photoluminescence (PL) measurements was performed with an Ar ion laser (514.5 nm) as the excitation source and the luminescence was detected with a silicon detector through a 0.75 m monochromator.
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RESULTS
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The PL spectra for samples irradiated with H to doses of 5 x 1014 cm- and 5 x 1015 cm 2 are shown in Fig. 1 (a) and (b) respectively. The spectra of the unirradiated samples are also shown for comparison. In all cases, the samples have been annealed at 900 'C for 30 s. No PL signal was detected just after irradiation prior to annealing due to the high density of defects which act as nonradiative recombination centres for the photoexcited holes and electrons. Four peaks are clearly resolved corresponding to the 4 QWs. The sharp peak and the smaller peaks at 810850 nm correspond to the emission from the GaAs buffer and/or substrate. As shown in Fig. 1 (a), the emission wavelengths of the four QWs are slightly shifted towards the higher energy end of the spectrum (blue shift) after irradiation and annealing. The recovery of the PL intensities is excellent and comparable to that of the unirradiated sample. However, there is evidence that some residual defects are still present after annealing as indicated by the slightly lower PL signals.
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Fig. 1 Low temperature PL spectra for samples irradiatedwith H to doses of (a) 5 x 1014 cm-2 and (b) 5 x 1015 cm-2. Both samples have been annealed. The spectra of the unirradiatedsamples are also shown for reference.
In Fig 1 (b), the irradiation dose is increased by an order of magnitude to 5 x 1015 cm 2 . Very large energy shifts are observed, in particular QW #2 and QW #3, have 113 meV and 100 meV shifts, respectively. It is interesting that the thinnest (QW #1) and the thickest well (QW #4) show about the same energy shift. This is quite surprising since one would expect the thinnest well to be the most sensitive to any perturbation. Another surprising result is that one would expect the PL intensity of this intermixed sample to drop by about a factor of ten as compared to the previous lower dose sample. However, this is not the case. In fact, the recovery of the PL intensities is quite good, only about a factor of two lower than that of the reference sample. A very large shift of about 200 meV w
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