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ArticleA series of Be ␦-doped GaAs/AlAs multiple-quantum wells with the doping at the well center were grown by molecular beam epitaxy. The photoluminescence spectra were measured at 4, 20, 40, 80, 120, and 200 K, respectively. The two-hole transitions of the acceptor-bound exciton from the ground state, 1S 3/2 (⌫ 6 ), to the first-excited state, 2S 3/2 (⌫ 6 ), have been clearly observed and the acceptor binding energy measured. A variational calculation is presented to obtain the acceptor binding energy as a function of well width. It is found that the experimental results are in good agreement with the theory.

We have investigated the effect of confinement on the shallow acceptor transitions in δ-doped GaAs/AlAs multiple-quantum wells with well widths ranging from 30 to 200 Å. A series of Be δ-doped GaAs/AlAs multiple-quantum wells with doping at the well center and a single epilayer of GaAs uniformly Be doped were grown by molecular beam epitaxy. Photoluminescence spectra were measured at 4, 20, 40, 80, 120, and 200 K, respectively. Two-hole transitions of the acceptor-bound exciton from the ground state, 1S3/2(Γ6), to the excited state, 2S3/2(Γ6), were clearly observed. It is found that the acceptor transition energy increases with a decrease in quantum well width.

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We report the observation of photoluminescence due to single InGaN dots using samples containing very low surface dot densities. InGaN dot samples were grown by metalorganic vapour phase epitaxy with varying surface dot densities, the lowest being below 1 per µm 2 . The dots are typically 30-40 nm in diameter and 4-6 nm in height. Photoluminescence spectra taken from large dot ensembles indicate a low energy tale to the InGaN layer emission, which increases in intensity as the dot density increases. The energy resolved photoluminescence lifetime indicates that low energy feature is long lived, a significant rise time for the low energy photoluminescence also indicates slow carrier relaxation. The use of 400 nm apertures in aluminium shadow masks allows the observation of sharp line features due to individual exciton localisation centres. Under low excitation powers the broadband InGaN epilayer emission is found to break up into very large number of sharp line features consistent with the presence of strong localisation excitons within the InGaN epilayer due to alloy fluctuations. In addition, on the low energy wing of the quantum well band, strong, isolated sharp emission lines are observed. Many such apertures containing single line emission spectra have been observed. 1 Introduction Semiconductor quantum dots are an area of great current interest. The zero dimensional potential created by the formation of nanoscale inclusions in a surrounding matrix offers the possibility of controlling the generation and transmission of individual carriers. Moreover, the presence of isolated (in energy) carrier eigenstates permits a wide range of fundamental physics experiments. The formation of quantum dots by the so-called Stranski-Krastonov growth mode has been observed in several III-V semicondcutor systems such as InAs/GaAs and InP/GaP. In these systems the formation of pyramidal quantum dots is essentially strain driven with the dot density and size only weakly dependent on the exact growth conditions. The formation of dots in the GaN/InGaN system is potentially very important for optoelectronic devices such as quantum dot lasers which are predicted to have a lower threshold current than conventional quantum well lasers. InN and GaN are immiscible in the bulk and the associated alloy In x Ga 1-x N can only be formed under highly non-equilibrium epitaxial growth conditions.