Acceptor energy levels in GaAs/AlGaAs quantum wells in the presence of an external magnetic field

Energy levels of ground- and excited shallow acceptor states in quantum wells (QWs) have been calculated in the presence of an external magnetic field within a four-band effective-mass theory, in which the valence-band mixing as well as the mismatch of the band parameters and the dielectric constants between well and barrier materials have been taken into account. The energy separations between the ground and different excited acceptor states are deduced at various magnetic fields. The g-factors of the acceptor 1S3/2 ground states and the 2P3/2 excited states are obtained for QWs with different well widths. The oscillator strengths of the acceptor infrared transitions in QWs corresponding to the G, D, and C lines of acceptors in bulk GaAs have also been calculated vs magnetic field up to 10 T

Temperature dependence of exciton-capture at impurities in GaAs/AlxGa(1-x) As quantum wells

In this paper we present an investigation of the exciton capture process in GaAs/Al.3Ga.7As quantum wells using a picosecond time-resolved photoluminescence technique. We demonstrate that there are significant differences in the capture mechanism for narrow quantum wells in comparison to bulk material. In particular the initial capture efficiency is shown to increase with temperature. This behaviour is understood in terms of the role of localisation of the free exciton in the potentials caused by the interface roughness. Higher temperatures destroy this localisation process which otherwise limits the total capture rate for the exciton to the impurity. The effect of localisation on capture is also shown to be stronger for narrower wells. We conclude that the relative weakness of bound exciton recombination in the near bandgap luminescence of doped quantum wells can in part be understood by the reduction of capture efficiency due to localisation

The electronic structure of a shallow acceptor and its bound exciton confined in GaAs/AlGaAs quantum wells

The exciton bound (BE) at the shallow Be acceptor confined in a narrow GaAs/AlGaAs quantum well (QW) has been investigated by means of selective photoluminescence (SPL) and PL excitation (PLE) experiments. For the shallow acceptor, several excited states have been observed as two-hole transition (THT) satellites of the BE. The heavy hole (hh)-like excited nS(Γ6) acceptor states dominate the satellite spectrum, but also the light hole (lh)-like excited 2S(Γ7) and the parity forbidden transition to the 2P3/2 excited state have been monitored in SPL spectra. When detecting a THT satellite, the 1S(Γ6) hh-like acceptor ground state has been spectrally resolved from the 1S(Γ7) lh-like state in PLE spectra. Several BE states have been theoretically predicted and observed in PLE spectra with the J=5/2 state at lowest energy, like in bulk GaAs. The proposed interpretation of the acceptor hh- and lh-states is confirmed by SPL and PLE experiments in the presence of an applied magnetic field and in polarized PLE measurements. An effective g-value for the acceptor BE recombination in varying degree of confinement is derived from these Zeeman measurements

Polarized micro-photoluminescence spectroscopy of GaN nanocolumns

International audienceWe propose inversion domains (IDs) to be the origin of the 3.42 eV photoluminescence (PL) band in GaN epilayers and nanocolumns. A shift of the band relatively to the near‐edge PL band is induced presumably by different strain in the IDs. Micro‐PL studies of nanocolumns enriched by IDs reveal anti‐correlated intensity variation as well as a similarity between temperature and power dependences of both bands. A change of dominant polarization takes place across the spectra, being likely related to variation of exciton level ordering at tensile strain. Discrete narrow lines observed in the spectra are considered as manifestation of strain‐induced one‐dimensional carrier confinement in the ID

Quantum dots-in-a-well infrared photodetectors for long wavelength infrared detection

We report on a quantum dots-in-a-well infrared photodetector (DWELL QDIP) grown by metal organic vapor phase epitaxy. The DWELL QDIP consisted of ten stacked InAs/In0.15Ga0.85As/GaAs QD layers embedded between n-doped contact layers. The density of the QDs was about 9 x 1010 cm-2 per QD layer. The energy level structure of the DWELL was revealed by optical measurements of interband transitions, and from a comparison with this energy level scheme the origin of the photocurrent peaks could be identified. The main intersubband transition contributing to the photocurrent was associated with the quantum dot ground state to the quantum well excited state transition. The performance of the DWELL QDIPs was evaluated regarding responsivity and dark current for temperatures between 15 K and 77 K. The photocurrent spectrum was dominated by a LWIR peak, with a peak wavelength at 8.4 µm and a full width at half maximum (FWHM) of 1.1 µm. At an operating temperature of 65 K, the peak responsivity was 30 mA/W at an applied bias of 4 V and the dark current was 1.2×10-5 A/cm2. Wavelength tuning from 8.4 µm to 9.5 µm was demonstrated, by reversing the bias of the detector