Electro- and photoluminescence spectra of high-brightness light-emitting AlGaN/InGaN/GaN single-quantum-well structures are studied over a broad range of temperatures and pumping levels. Blue shift of the spectral peak position was observed along with an increase of temperature and current. An involvement of band-tail states in the radiative recombination was considered, and a quantitative description of the blue temperature-induced shift was proposed assuming a Gaussian shape of the band tail.

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A dramatic increase of the conduction band electron mass in a nitrogen-containing III–V alloy is reported. The mass is found to be strongly dependent on the nitrogen content and the electron concentration with a value as large as 0.4m0 in In0.08Ga0.92As0.967N0.033 with 6×1019 cm−3 free electrons. This mass is more than five times larger than the electron effective mass in GaAs and comparable to typical heavy hole masses in III–V compounds. The results provide a critical test and fully confirm the predictions of the recently proposed band anticrossing model of the electronic structure of the III–N–V alloys.

O and Si donors in GaN are studied by Raman spectroscopy under hydrostatic pressure p. The ground state of O is found to transfer from a shallow level to a deep gap state at p . 20 GPa reminiscent of DX centers in GaAs. Transferred to Al x Ga 12x N we predict that O induces a deep gap state for x . 0.40. In GaN:Si no such state is induced up to the highest pressure obtained ͑p 25 GPa͒ equivalent to x 0.56 in Al x Ga 12x N and possibly higher. We attribute this distinction to the lattice sites of the dopants. O substituting for N is found to be the origin of high free electron concentration in bulk GaN crystals. [S0031-9007(97)03179-7] PACS numbers: 71.55. Eq, 62.50.+ p, 72.20.Jv, 78.30.Fs Donors in III-V compound semiconductors are of special interest because they can assume both extended or localized states, i.e., they can be metastable [1][2][3][4]. In the most thoroughly studied system, GaAs, either a high free carrier concentration n, alloying with AlAs, or application of hydrostatic pressure p can induce a transition from a shallow hydrogenic state of the dopant to a strongly localized one of the same impurity. Many different donor species, e.g., Si Ga (group-IV element on group-III site) and S As (group-VI on group-V site), transform into the nonhydrogenic configuration at very similar characteristic transition pressures [3,4]. In addition, metastability effects, such as a limited free electron concentration and persistent photoconductivity, have been found and interpreted with activation barriers between the different configurations of the donor. All of these effects have been associated with a so-called DX center [2].In GaN we find that the O donor dopant shows characteristic features of a DX defect when hydrostatic pressure is applied. Si, in contrast, behaves like a hydrogenic donor. This distinction is attributed to the actual lattice site of the impurity, and this effect is extremely pronounced in this compound semiconductor system. The pressure experiments can directly be transferred from GaN to the Al x Ga 12x N system predicting a strongly localized gap state of O for higher Al concentrations.Dopant impurities typically can induce both resonant and hydrogenic defect levels in the electronic band structure. In many cases only the hydrogenic level is relevant. Under certain conditions, however, a charge transfer from a quasihydrogenic state to a strongly localized neutral charge state ͑D 0 ͒ can occur [5]. In addition, as proposed by Chadi and Chang [1], a structural relaxation of the donor impurity in the vicinity of the transition conditions can lead to an activation barrier between the two states. This widely accepted model of a structural relaxation explains the metastability and the activation barrier between the different states of DX centers. Promoted by the transfer of electrons, this new strongly localized state (DX) can be the ground state [6]. Ab initio calculations reproduce the experimental observations in GaAs, including the very similar transition conditions found for all substituti...

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We report a cross-correlated investigation, performed by means of Raman scattering and infrared spectroscopy, of coupled LO phonon-plasmon modes in bulk GaN. Using different samples with different (high) residual concentrations of free carriers, we find that the high-energy Raman mode follows closely the plasma frequency resolved from the infrared data. On the opposite, the low-frequency modes appears down shifted, with respect to the standard TO phonon frequency, by about 11 cm−1. Both findings agree satisfactorily with predictions of the linear response theory for undamped phonon-plasmon modes and establish Raman scattering as a powerful and nondestructive tool to investigate the residual doping level of GaN up to about 1020 cm−3 .

We investigated the pressure behavior of yellow luminescence in bulk crystals and epitaxial layers of GaN. This photoluminescence band exhibits a blueshift of 30±2 meV/GPa for pressures up to about 20 GPa. For higher pressure we observe the saturation of the position of this luminescence. Both effects are consistent with the mechanism of yellow luminescence caused by electron recombination between the shallow donor (or conduction band) and a deep gap state of donor or acceptor character.

Electrical and optical properties of Nichia double-heterostructure blue light-emitting diodes, with In 0.06 Ga 0.94 N:Zn, Si active layer, are investigated over a wide temperature range from 10 to 300 K. Current-voltage characteristics have complex character and suggest the involvement of various tunneling mechanisms. At small voltages ͑and currents͒, the peak wavelength of the optical emission shifts with the applied bias across a large spectral range from 539 nm ͑2.3 eV͒ up to 443 nm ͑2.8 eV͒. Light emission takes place even at the lowest temperatures, indicating that a complete carrier freeze-out does not occur.