The hole effective-mass Hamiltonian for the semiconductors with wurtzite structure is given. The effective-mass parameters are determined by fitting the valence-band structure near the top with that calculated by the empirical pseudopotential method. The energies and corresponding wave functions are calculated with the obtained effective-mass Hamiltonian for the CdSe quantum spheres, and the energies as functions of sphere radius R are given for the zero spin-orbital coupling (SOC) and finite SOC cases. The energies do not vary as 1/R² as the general cases, which is caused by the crystal-field splitting energy and the linear terms in the Hamiltonian. It is found that the ground state is not the optically active S state for the R smaller than 30Å, in agreement with the experimental results and the “dark exciton” theory. © 1999 The American Physical Society.

Xia Jian-Bai;Li Jingbo

Physical Review B Condensed Matter and Materials Physics

1999

The electronic properties of wide-energy gap zinc-blende structure GaN, AlN, and their alloys Ga1-xAlxN are investigated using the empirical pseudopotential method. Electron and hole effective mass parameters, hydrostatic and shear deformation potential constants of the valence band at Γ and those of the conduction band at Γ and X are obtained for GaN and AlN, respectively. The energies of Γ, X, L conduction valleys of Ga1-xAlxN alloy versus Al fraction x are also calculated. The information will be useful for the design of lattice mismatched heterostructure optoelectronic devices based on these materials in the blue light range application. ©1996 American Institute of Physics.

Fan W. J.;Li M. F.;Chong T. C.;Xia J. B.

Journal of Applied Physics

1996

By using the hole effective-mass Hamiltonian for semiconductors with the wurtzite structure, we have studied the exciton states and optical spectra in CdSe nanocrystallite quantum dots. The intrinsic asymmetry of the hexagonal lattice structure and the effect of spin-orbital coupling (SOC) on the hole states are investigated. It is found that the strong SOC limit is a good approximation for hole states. The selection rules and oscillator strengths for optical transitions between the conduction- and valence-band states are obtained. The Coulomb interaction of exciton states is also taken into account. In order to identify the exciton states, we use the approximation of eliminating the coupling of Γ6(X, Y) with Γ1(Z) states. The results are found to account for most of the important features of the experimental photoluminescence excitation spectra of Nonris et al. However, if the interaction between Γ6(X, Y) and Γ1(Z) states is ignored, the optically passive Px state cannot become the ground hole state for small CdSe quantum dots of radius less than 30 Å. It is suggested that the intrinsic asymmetry of the hexagonal lattice structure and the coupling of Γ6(X, Y) with Γ1(Z) states are important for understanding the "dark exciton" effect. © 2000 The American Physical Society.

Li Jingbo;Xia Jian-Bai

Physical Review B Condensed Matter and Materials Physics

2000

The valence hole subbands. TE and TM mode optical gains, transparency carrier density, and radiative current density of the zinc-blende GaNA/Ga0.85Al0.15N strained quantum well (100 Å well width) have been investigated using a 6×6 Hamiltonian model including the heavy hole, light hole, and spin-orbit split-off bands. At the k=0 point, it is found that the light hole strongly couples with the spin-orbit split-off hole, resulting in the so+lh hybrid states. The heavy hole does not couple with the light hole and the spin-orbit split-off hole. Optical transitions between the valence subbands and the conduction subbands obey the Δn=0 selection rule. At the k ≠ 0 points, there is strong band mixing among the heavy hole, light hole, and spin-orbit spin-off hole. The optical transitions do not obey the Δn=0 selection rule. The compressive strain in the GaN well region increases the energy separation between the sol+lh1 energy level and the hh1 energy level. Consequently, the compressive strain enhances the TE mode optical gain, and strongly depresses the TM mode optical gain. Even when the carrier density is as large as 10¹⁹ cm^-3, there is no positive TM mode optical gain. The TE mode optical gain spectrum has a peak at around 3.26 eV. The transparency carrier density is 6.5×10¹⁸ cm^-3, which is larger than that of GaAs quantum well The compressive strain overall reduces the transparency carrier density. The Jrad is 0.53 kA/cm² for the zero optical gain. The results obtained in this work will be useful in designing quantum well GaN laser diodes and detectors. © 1996 American Institute of Physics.

Fan W. J.;Li M. F.;Chong T. C.;Xia J. B.

Journal of Applied Physics

1996

Quantum-confined Stark effects are investigated theoretically in (Formula presented) quantum wires formed in V-grooved structures. The electronic structures of the V-shaped quantum wires are calculated within the effective mass envelope function theory in the presence of electric field. The binding energies of excitons are also studied by two-dimensional Fourier transformation and variational method. The blue Stark shifts are found when the electric field is applied in the growth direction. A possible mechanism in which the blueshifts of photoluminescence peaks are attributed to two factors, one factor comes from the asymmetric structure of quantum wire along the electric field and another factor arises from the electric-field-induced change of the Coulomb interaction. The numerical results are compared with the recent experiment measurement. © 1998 The American Physical Society.

Chang Kai;Xia J.

Physical Review B Condensed Matter and Materials Physics

1998

Quantum-confined Stark effects in InAs/GaAs self-assembled quantum dots are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels and optical transition energies are calculated in the presence of perpendicular and parallel electric field. In our calculation, the effect of finite offset, valence band mixing, and strain are all taken into account. The results show that the perpendicular electric field weakly affects the electron ground state and hole energy levels. The energy levels are affected strongly by the parallel electric field. For the electron, the energy difference between the ground state and the first excited state decreases as electric field increases. The optical transition energies have clear redshifts in electric field. The theoretical results agree well with the available experimental data. Our calculated results are useful for the application of quantum dots to photoelectric devices. © 2000 American Institute of Physics.

Li Shu-Shen;Xia Jian-Bai

Journal of Applied Physics

2000

In the framework of effective mass envelope function theory, absorption coefficients are calculated for intraband (intersubband in the conduction band) optical transition in InAs/GaAs coupled quantum dots. In our calculation the microscpic distributon of the strain is taken into account. The absorption in coupled quantum dots is quite different from that of superlattices. In superlattices, the absorption does not exist when the electric vector of light is parallel to the superlattice plane (perpendicular incident). This introduces somewhat of a difficulty in fabricating the infrared detector. In quantum dots, the absorption exists when light incident along any direction, which may be good for fabricating infrared detectors. © 1997 The American Physical Society.

Li Shu-Shen;Xia Jian-Bai

Physical Review B Condensed Matter and Materials Physics

1997

Electronic structures of semimetal-semiconductor superlattices made of GdAs and GaAs are studied by a second-neighbor tight-binding model. It is found that this semimetal-semiconductor superlattice is metallic with overlapping conduction and valence bands for GdAs layers as thin as two monolayers. This is in qualitative agreement with recent experimental observation. The superlattice states with energies near the Fermi surface consist of states derived from the GdAs valence bands and the lowest GdAs conduction bands with wave vectors near point X. It is shown that the two types of superlattice energy bands can be simulated by a more sophisticated effective-mass theory with anisotropic, energy-dependent effective masses. © 1991 The American Physical Society.

Xia Jian-Bai;Ren Shang-Fen;Chang Yia-Chung

Physical Review B

1991

In the framework of the effective-mass envelope-function theory, the electronic and optical properties of a spherical core-shell quantum-dot quantum well (QDQW) structure with one and two wells have been investigated. The results show that the energies of electron and hole states depend sensitively on the well thickness and core radius of quantum-dot quantum well structure. An interesting spatially separated characteristic of electron and hole in QDQW is found and enhanced significantly in the two-wells case. The normalized oscillator strength for the optical transition between the electron and hole states in QDQW exhibits a deep valley at some special well thickness. The Coulomb interaction between the electron and hole is also taken into account. © 1998 The American Physical Society.

Chang Kai;Xia Jian-Bai

Physical Review B Condensed Matter and Materials Physics

1998

In this article, we give the electronic structure and optical transition matrix elements of coupled quantum dots (QDs) arranged as different cubic lattices: simple cubic (sc), body-centered cubic (bcc), and face-centered cubic (fee) superlattices. The results indicate that electron and hole energies of bcc, sc, and fee superlattices are the lowest, the highest, and the middle, respectively, for the same subband under the same QD density or under the same superlattice constant. For a fixed QD density, the confinement effects in sc, fcc, and bcc superlattices are the strongest, the middle, and the weakest, respectively. There are only one, two, and four confined energy bands, with energies lower than the potential barrier for sc, bcc, and fcc QD superlattices, respectively. The results have great significance for researching and making semiconductor quantum dot devices. © 1998 American Institute of Physics.

Li Shu-Shen;Xia Jian-Bai

Journal of Applied Physics

1998