J.-B. Jeon

Piezoelectric effect on optical properties of pseudomorphically strained wurtzite GaN quantum wells

The presence of internal strain in wurtzite quantum-well (QW) structures may lead to the generation of large polarization fields. These piezoelectric fields cause a spatial separation of the electrons and holes inside the QW to screen the internal fields. A self-consistent calculation of optical gain and the corresponding differential gain is presented in pseudomorphically strained GaN quantum wells as a function of carrier density. Based on the local exchange-correlation potential, electron and hole band structures are obtained by coupling Poissons equation with an effective-mass Schrodinger equation in the conduction band and an envelope-function (or k/spl middot/p) Hamiltonian in the valence band. Our calculations show that self-consistent calculations including the piezoelectric effects are essential for accurate description of strained wurtzite QW structures.

Strain effects on valence band structure in würtzite GaN quantum wells

The effect of strain on valence band spectra in both bulk and in pseudomorphic GaN quantum wells is studied theoretically using recent experimental results for deformation potential constants. Wave functions and dispersion curves for A‐, B‐ and C‐hole subbands are obtained from linear combination of bulk analytical solutions for the 3×3 wurtzite block‐Hamiltonian. A detailed analysis is presented for the dependence of hole spectrum on quantum well width, depth, and strain due to lattice mismatch.

Strain effects on optical gain in wurtzite GaN

Strain effects on optical gain in hexagonal bulk GaN are calculated and explained in terms of the change in the effective hexagonal crystal field component. Qualitatively, even unstrained wurtzite structures correspond to cubic crystals with a proper biaxial stress applied. Such biaxial stress results in effective tensile deformation along the c axis ([111] direction in cubic crystals) and compressive strain in the perpendicular plane. Therefore, the light mode with a polarization vector parallel to the c axis is suppressed, while the mode with a perpendicular polarization is enhanced in wurtzite structures. Thus, compared to cubic structures with similar material parameters, a strong optical anisotropy of wurtzites results in enhanced gain for certain light polarizations, which make wurtzite structures superior for lower-threshold lasing. These qualitative arguments are illustrated by numerical calculations of optical gain in biaxially strained wurtzite GaN, based on a 6×6 envelope-function Hamiltonian.

Valence band parameters of wurtzite materials

Abstract We deduced the valence band parameters of several wurtzite materials (ZnS, CdS, CdSe, and GaN) by matching the results of existing full-band calculations of the energy spectrum with analytical expressions of the envelope-function formalism. The calculated A-, B-, and C-type hole dispersion relations show strongly anisotropic characteristics and anti-crossing features in spectrum due to band mixing effects. We demonstrated that for all materials considered except CdSe, the spherical cubic approximation for six Luttinger-like parameters holds with good accuracy, so that the anisotropy arises mainly owing to the crystal field splitting term. Thus, the top valence band may be described with (in addition to crystal field and spin-orbit splitting energies) only two Luttinger-like parameters, γ 1 and γ 2 .

OPTOELECTRONIC PROPERTIES OF STRAINED WURTZITE GaN QUANTUM-WELL LASERS

Fundamental optical properties of strained wurtzite GaN quantum-well laser are calculated and evaluated near the threshold condition. The formalism is based on a self-consistent methodology that couples an envelope-function Hamiltonian for band structures with photon-carrier rate equations. Details of energy band structure, optical gain, and modulation response are studied comprehensively under the effects of strain-induced piezoelectric fields, bandgap renormalization, and the carrier capture processes. Comparisons between different approximations show that self-consistency is essential to accurately simulate pseudomorphically strained wurtzite GaN quantum-well lasers.