Petr G. Eliseev

“Blue” temperature-induced shift and band-tail emission in InGaN-based light sources

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.

Transition dipole moment of InAs/InGaAs quantum dots from experiments on ultralow-threshold laser diodes

Semiconductor ultralow-threshold InAs quantum-dot lasers are investigated operating at 1230–1250 nm at room temperature (laser threshold range is of 16–83 A/cm2 for ground-state emission). The dependence of gain on current is derived from measurements of the threshold current as a function of the cavity length. The ground-state gain appears at very low current: the inversion threshold of ∼13 A/cm2 is a record low value. Analysis of these data for diodes of different molecular beam epitaxial-grown wafers leads to a squared dipole moment of the transition of ∼9.2×10−57 C2 m2 that corresponds to the length of elementary dipole of ∼0.6 nm.

Low‐temperature study of current and electroluminescence in InGaN/AlGaN/GaN double‐heterostructure blue light‐emitting diodes

Electrical and optical properties of Nichia double‐heterostructure blue light‐emitting diodes, with In0.06Ga0.94N: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 currents), the peak wavelength of the optical emission shifts with the applied bias across a large spectral range from 539 nm (2.3 eV) up to 443 nm (2.8 eV). Light emission takes place even at the lowest temperatures, indicating that a complete carrier freeze‐out does not occur.

Ground-state emission and gain in ultralow-threshold InAs-InGaAs quantum-dot lasers

Emission spectra and modal optical gain are investigated in ultralow-threshold MBE-grown InAs-InGaAs quantum dot (QD) structures. The record lowest room-temperature inversion current is found to be /spl sim/13 A cm/sup -2/. The rate-equation model is proposed describing the optical gain related to the ground-state (GS) transitions in QDs. The ground-state gain goes to the maximum value that corresponds to the total inversion of available levels. The gain cross section for the GS emission is estimated as /spl sim/7/spl times/10/sup -15/ cm/sup 2/.

Comparison of the carrier induced refractive index, gain, and linewidth enhancement factor in quantum dot and quantum well lasers

The spectral dependence of the modal gain and linewidth enhancement factor is measured in an InAs/GaInAs/AlGaAs/GaAs quantum dot (QD) laser and a GaInAs/AlGaAs/GaAs quantum well laser of the same design lacking only the quantum dots. The material differential gain and material differential carrier induced refractive index are found to be about three times smaller in the quantum dot laser than in the quantum well laser. The linewidth enhancement factor is smaller in the QD laser and exhibits considerably less dispersion.

Influence of pressure on photoluminescence and electroluminescence in GaN/InGaN/AlGaN quantum wells

We have measured photoluminescence and electroluminescence in two different types of high-brightness single-quantum-well light emitting diodes manufactured by Nichia Chemical Industries with InxGa1−xN active layers (x=0.45 and x=0.15), under hydrostatic pressures up to 8 GPa. We discovered that the pressure shift of the primary luminescence peak in each diode is very small: 12 and 16 meV/GPa for the green and blue diodes, respectively. The observed pressure coefficients are much lower than those characteristic of the energy gap in GaN (≈40 meV/GPa) or the energy gap in InN (≈33 meV/GPa). This kind of behavior is usually associated with recombination processes involving localized states. These localized states may be associated either with band tails (arising from In fluctuations in the active layer or from high density of defects), and/or with localized excitons of various types.

Thermal activation of excitons in asymmetric InAs dots-in-a-well InxGa1−xAs∕GaAs structures

Photoluminescence, its temperature dependence, and photoluminescence excitation spectra of InAs quantum dots embedded in asymmetric InxGa1−xAs∕GaAs quantum wells [dots in a well (DWELL)] have been investigated as a function of the indium content x (x=0.10–0.25) in the capping InxGa1−xAs layer. The asymmetric DWELL structures were created with the aim to investigate the influence of different barrier values at the quantum dot (QD)/quantum well interface on the photoluminescence thermal quenching process. The set of rate equations for the two stage model for the capture and thermal escape of excitons in QDs are solved to analyze the nature of thermal activation energies for the QD photoluminescence quenching process. The two stage model for exciton thermal activation was confirmed experimentally in the investigated QD structures as well. The localization of nonradiative defects in InAs∕InGaAs DWELL structures is discussed on the base of comparison of theoretical and numerically calculated (fitting) results.

Recombination balance in green-light-emitting GaN/InGaN/AlGaN quantum wells

Recombination balance parameters for GaN/InGaN/AlGaN single-quantum-well green-lightemitting diodes are extracted from optical power and carrier lifetime measurements. The radiative recombination coefficient B is found to depend on two-dimensional carrier density N, with a low-carrier-density limit of B0=1.2×10−4 cm2/s. Sublinearity of the light–current characteristic at temperatures ⩾300 K is associated with a nonradiative process whose rate is proportional to ∼N4.8. The external quantum efficiency of 5.5% at 20 mA results from the internal quantum yield of 63% and the photon extraction efficiency of 8.7%. At low temperatures, a nonradiative loss term proportional to ∼N9 is also identified.

Effect of silicon doping on the optical and transport properties of InGaN/GaN multiple-quantum-well structures

Temperature-dependent photoluminescence and transport measurements were performed on the In0.13Ga0.87N:Si/GaN:Si multiple-quantum-well (MQW) structures with different doping levels. By fitting the temperature-dependent emission energy of these samples using the band tail model, an obvious localization effect is observed in lightly doped MQW structures. Correspondingly, the electron mobilities in these structures are significantly higher than those of undoped and heavily doped MQW structures. Furthermore, when the localization effect is stronger, the mobility is higher.

Orientation dependence of the optical properties in InAs quantum-dash lasers on InP

The anisotropy of the modal gain and the linewidth enhancement factor was experimentally measured in InAs/AlGaInAs/InP semiconductor lasers with an active region composed of quantum confined structures in the form of short wires called quantum dashes. This anisotropy is due to the polarization dependence of the transition matrix element in these quantum nanostructures. The spectral dependence of the gain and linewidth enhancement factor was investigated in a wavelength range from 1540 to 1640 nm at subthreshold current densities. The largest gain and the smallest linewidth enhancement factor were obtained when the quantum dashes were oriented perpendicular to the axis of the laser cavity.