K. K. Bajaj

Energy levels of hydrogenic impurity states in GaAs-Ga1−xAlxAs quantum well structures

Abstract Binding energies of the ground state and of four excited states of a hydrogenic impurity in quantum well structures consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga1−xAlxAs are calculated using a variational approach. The ground-state binding energy is calculated as a function of the barrier potential for a given size of the GaAs quantum well and is found to be linearly dependent on the inverse of the square root of the barrier potential except for very small potentials. The variation of the binding energies of all five states as a function of the size of the GaAs quantum well are also calculated and their behavior is discussed.

Shallow impurity centers in semiconductor quantum well structures

Abstract Interest in the study of the behavior of shallow impurity centers in superlattices and quantum well structures is fairly recent. This paper reviews briefly both the theoretical and experimental work done in this field in the last few years. Several recent calculations of the energy levels of hydrogenic impurity states in quantum well structures, such as Ga1−xAlxAsGaAsGa1−xAlxAs, are reviewed. The behavior of these levels as a function of the quantum well size is discussed. Recent experimental data concerning the variations of the binding energies of shallow donors and acceptors as a function of the GaAs quantum well size are reviewed. A comparison between these experimental measurements and the results of recent calculations is presented.

Temperature dependence of sharp line photoluminescence in GaAsAl0.25Ga0.75As multiple quantum well structures

Abstract Photoluminescence properties of sharp emission lines (the heavy- and light-hole excitons, the excitons bound to neutral donor and acceptor, and the heavy hole-to-neutral donor transition) present in high quality GaAsAl0.25Ga0.75As multiple-quantum well structures have been determined as a function of temperature from 2 to 296 K. The four multiple- quantum well structures studied each consist of 100, 200, 300 and 400 A GaAs wells separated by 100 A Al0.25Ga0.75As barriers. The exciton bound to a neutral donor located at the center of the well is suggested to be the predominant photoluminescence emission in the temperature range of 2–296 K. The photoluminescence in the peak region consists mainly of the heavy-hole exciton and donor-bound excitons.

Observation of discrete donor-acceptor pair spectra in MBE grown GaAs

Abstract We report the first observation of discrete donor-acceptor pair photo- luminescence spectra in GaAs. Sixty sharp lines are observed in the region between 1.5110-1.5040 eV. These are interpreted as discrete donor- acceptor pair lines resulting from preferential pairing. The pairs are believed to result from silicon on the gallium sublattice and carbon on the arsenic sublattice.

Photocurrent spectroscopy of InxGa1−xAs/GaAs multiple quantum wells

Photocurrent spectra of InxGa1−xAs/GaAs multiple quantum well structures grown by molecular beam epitaxy are studied in the presence of electric fields perpendicular to the heterointerface. Several Δn=0 allowed and Δn≠0 forbidden excitonic transitions are observed. Both negative and positive shifts of exciton transitions are found. Good agreement is found between the photocurrent observations and calculations using a multiband effective‐mass approach, taking into account the strain‐induced splitting.

Binding energies of Wannier excitons in GaAs-Ga1−xAlxAs quantum well structures

Abstract Binding energies of Wannier excitons in a quantum well structure consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga 1− x Al x As are calculated using a variational approach. Due to reduction in symmetry along the axis of growth of these quantum well structures and the presence of band discontinuities at the interfaces, the degeneracy of the valence band of GaAs is removed leading to two exciton systems, namely, the heavy hole exciton and the light hole exciton. The variations of the binding energies of these two excitons as a function of the size of the GaAs quantum wells for various values of the heights of the potential barrier are calculated and their behavior is discussed.

Polaronic excitons inZnxCd1−xSe/ZnSequantum wells

We present a detailed investigation of excitonic absorption in

Energy levels of a hydrogenic donor in GaAs-GaAlAs quantum well structures in a magnetic field

Zn_{0.69}Cd_{0.31}Se/ZnSe

Energy levels of hydrogenic impurities and Wannier excitons in quantum well structures

quantum wells under the application of a perpendicular magnetic field. The large energy separation between heavy- and light-hole excitons allows us to clearly resolve and identify magneto-excitonic absorption resonant with the continuum edge of the 1S heavy-hole exciton. Experimental values of the exciton binding energy are compared with results of a theoretical model that includes the exciton-phonon interaction. The remarkable agreemeent found unambiguously indicates the predominant polaronic character of excitons in ZnSe-based heterostructures.

Refractive index, n, and dispersion, −dn/dλ, of GaAs at 2 K determined from Fabry–Perot cavity oscillations

Binding energies of the ground state (1s) and of excited states (2p±) of a hydrogenic donor associated with the lowest electron subband in a GaAs quantum well sandwiched between two semi-infinite layers of Ga1−xAlxAs, are calculated as a function of the size of the well in the presence of an arbitrary magnetic field. A variational approach is followed and these energy levels are calculated for a finite value of the height of the potential barrier. The positively charged ion of the donor atom is assumed to be located at the center of the well and the applied magnetic field is taken to be parallel to the axis of growth of the quantum well structure. As expected, for a given value of the magnetic field, the binding energies are found to be larger than their values in a zero magnetic field. The contribution to the binding energy of a given state due to the magnetic field, at a given field, increases slowly as the well size is reduced.