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We have performed longitudinal magnetoresistance measurements on heavily n-doped silicon for donor concentrations exceeding the critical value for the metal-nonmetal transition. The results are compared to those from a many-body theory where the donor electrons are assumed to reside at the bottom of the many-valley conduction band of the host. Good qualitative agreement between theory and experiment is obtained.

In this work, we present a systematic study of photoluminescence (PL), photoluminescence excitation (PLE) and resonant photoluminescence on AlGaAs/GaAs selectively doped quantum well structures, in order to better understand the optical properties of these systems. To support the interpretation of our experimental results we have calculated the confined states for the systems in the effective mass approximation, taking into account many body effects, such as exchange and correlation in the local density approximation.

The photogenerated carrier-induced band-edge modifications of beryllium single ␦-doped GaAs layers comprising a two-dimensional hole gas ͑2DHG͒ were investigated by means of photoluminescence, selective photoluminescence, and photoluminescence excitation spectroscopies. The results show direct evidence for a photoinduced electron confinement effect, which strongly enhances the radiative-recombination probability between electrons and holes of the 2DHG at low temperatures. ͓S0163-1829͑99͒01607-0͔Delta-doped structures have already been extensively investigated as they represent the state of the art in doping profile and became quite important for the microelectronic industry. 1 Although the n-type ␦-doping structures have received a great deal of attention so far, only recent the p-type ␦-doping structures became the subject of systematic investigations. 2-4 One remarkable contrast between these two systems is the fact that in photoluminescence ͑PL͒ measurements carried out on single isolated ␦-doped layers, the expected two-dimensional ͑2D͒ emission bands are only observed in p-type, but not in n-type structures. Moreover, the observed temperature dependence of the PL emission bands associated with the two-dimensional hole gas ͑2DHG͒ in p-type ␦-doped layers exhibits an interesting thermal quenching effect that has attracted interest recently. [4][5][6] It has been argued that the thermal quenching (T ϳ60 K) of the 2DHG-related emission band from p-type ␦-doped GaAs layers was probably due to the escape of holes from the ␦-potential well to the nearby bulk material. 6 However, the rapid thermal quenching (Tϳ12 K) observed in p-type Si layers by Buyanova and co-workers was explained in terms of a shallow electron-potential well induced by photoexcited holes, which are captured by the ␦-doping well. 4 According to this model, the quenching of the 2DHG luminescence is due to the thermal activation of confined electrons from the photoinduced-potential well to the continuous states in the host material.The comparison between the luminescence spectra from n-and p-type ␦-doping GaAs structures was recently performed through rigorous self-consistent band-structure calculations. 5 It was particularly emphasized the role played by the photoinduced electron-confinement effect on the realistic description of the PL spectra from p-type ␦-doped structures. In the present paper we report on the results obtained by means of PL, selective photoluminescence ͑SPL͒, and photoluminescence excitation ͑PLE͒ spectroscopies of Be ␦-doped GaAs structures. The aim of the paper is to provide direct evidence for such photoinduced effect as proposed by Buyanova and co-workers and confirmed by theory. A set of three samples was grown by molecular beam epitaxy on a semi-insulating GaAs ͑001͒ substrate. The samples comprise a 0.42-m-thick GaAs buffer layer, a plane of Be atoms, a 0.18-m-thick undoped GaAs layer, and a 50-A-thick Be-doped GaAs cap layer ( pϭ2 ϫ10 18 cm Ϫ3 ). The growth temperature was 580°C for the buffer layer and 520°C for t...

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