S.G. Spruytte

Incorporation of nitrogen in nitride-arsenides: Origin of improved luminescence efficiency after anneal

A key to the utilization of nitride-arsenides for long wavelength optoelectronic devices is obtaining low defect materials with long nonradiative lifetimes. Currently, these materials must be annealed to obtain device quality material. The likely defect responsible for the low luminescence efficiency is associated with excess nitrogen. Photoluminescence and capacitance–voltage measurements indicate the presence of a trap associated with excess nitrogen which decreases in concentration upon anneal. Our films are grown by elemental source molecular beam epitaxy and the background impurity concentration is low, thus we have investigated the role of crystalline defects. High resolution x-ray diffraction showed improved crystal quality after anneal. We observed that the lattice parameter does not decrease linearly with nitrogen concentration for levels of nitrogen above 2.9 mol % GaN. The fact that Vegard’s law is not observed, despite theoretical calculations that it should, indicates that nitrogen incorporat...

Electrical depth profile of p-type GaAs/Ga(As, N)/GaAs heterostructures determined by capacitance–voltage measurements

Capacitance–voltage measurements on metal-semiconductor contacts are used to examine depth-resolved electrical characteristics of GaAs/Ga(As, N)/GaAs heterostructures. The experimental depth profiles of the carrier concentration are compared with calculations based on self-consistent solutions of the Poisson equation. As-grown Ga(As, N) layers are p type, and hole concentrations of about 3×1016 cm−3 are observed for undoped Ga(As, N) layers with a GaN mole fraction of 3% and thicknesses below 80 nm. This hole concentration is stable during rapid thermal annealing. For a GaN mole fraction of about 3%, the valence band offset between GaAs and Ga(As, N) is found to be +(11±2) meV. The heterointerfaces are of type I. The dominant carrier depletion in as-grown heterostructures is due to donor-like defect levels, which are accumulated at the GaAs-on-Ga(As, N) interface. The amount of these interfacial defects rises remarkably in thicker Ga(As, N) layers, but can be completely removed by rapid thermal annealing ...

Origin and annealing of deep-level defects in p-type GaAs/Ga(As,N)/GaAs heterostructures grown by molecular beam epitaxy

Deep-level defects in p-type GaAs/Ga(As,N)/GaAs heterostructures grown by molecular beam epitaxy are investigated by deep-level transient Fourier spectroscopy. Depth-resolved distributions of hole traps are measured in as-grown and annealed heterojunctions in order to identify the defects, which lead to the degradation of the Ga(As,N) properties. Four defects are recognized in the heterostructures studied. Two dominant hole traps are found in Ga(As,N) at energies of about 0.35 and 0.45 eV above the valence band edge. These midgap levels originate from copper- and iron-related defects, the formation of which is connected with operation of the nitrogen plasma cell during Ga(As,N) growth. Both traps, which are removed by annealing, are discussed as the possible nonradiative centers that deteriorate the optical properties. Two other hole traps of intrinsic origin are related to the GaAs growth conditions close to the Ga(As,N)-on-GaAs interface, where the GaAs growth is affected by the nitrogen plasma despite ...

Electron traps in Ga(As,N) layers grown by molecular-beam epitaxy

Deep levels in the upper half of the band gap of strained Ga(As,N) with a GaN mole fraction of 3% are examined by deep-level transient Fourier spectroscopy on GaAs/Ga(As,N)/GaAs heterojunctions grown by molecular-beam epitaxy. In as-grown structures, we find a dominant electron trap at 0.25 eV below the conduction bandedge with a concentration above 1017 cm−3. Its capture cross section of about 10−17 cm2 for electrons is too small for an efficient nonradiative recombination center in Ga(As,N). According to theoretical predictions, this level is most likely connected with a nitrogen-split interstitial defect (N–N)As. The giant concentration of this trap can be strongly reduced by rapid thermal annealing.

Admittance dispersion of n-type GaAs/Ga(As, N)/GaAs heterostructures grown by molecular beam epitaxy

The electrical admittance of rectifying metal–semiconductor contacts on n-type GaAs/Ga(As, N)/GaAs heterostructures depends strongly on frequency and temperature. The distinct dispersion is due to the relatively high diffusion barrier around the Ga(As, N) layer. As long as the admittance is controlled by electrons inside the Ga(As, N) layer, their response to the ac electric field is dependent on frequency and temperature. Under appropriate conditions, capacitance–voltage measurements can be used to examine depth-resolved electrical characteristics of n-type GaAs/Ga(As, N)/GaAs heterostructures. The experimental depth profiles of the carrier concentration are compared with calculations based on self-consistent solutions of the Poisson equation. For 3% GaN mole fraction, the conduction band offset between GaAs and Ga(As, N) is found to be −(0.40±0.01) eV, i.e., about 95% of the total band gap difference. The heterointerfaces are of type I. At the Ga(As, N)-on-GaAs interface, negative charges of about 1.3×1...

Low-threshold oxide-confined GaInNAs long wavelength vertical cavity lasers

We report, for the first time, room temperature continuous-wave (CW) operation of GaInNAs vertical-cavity surface-emitting laser diodes emitting at a wavelength of 1.2 /spl mu/m and grown all-epitaxially in a single step on a GaAs substrate. Oxide-apertured devices demonstrated CW threshold currents as low as 1 mA, slope efficiency above 0.045 W/A, and thermal impedance of 1.24 K/mW. Larger sized devices exhibited a pulsed threshold current density of 2-2.5 kA/cm/sup 2/ and slope efficiency above 0.09 W/A.

Group III nitride–arsenide long wavelength lasers grown by elemental source molecular beam epitaxy

Elemental source molecular beam epitaxy was used to grow InGaNAs quantum well samples, edge-emitting laser diodes, and vertical-cavity laser diodes on GaAs substrates. The quantum well samples exhibited an as-grown room temperature photoluminescence peak beyond 1310 nm which both increased dramatically in intensity and blueshifted with thermal annealing. Edge emitting laser diodes had threshold current densities as low as 450 and 750 A/cm2 for single and triple quantum well active regions, respectively, and emitted light at 1220–1250 nm. The vertical cavity laser diodes emitted light at 1200 nm and had threshold current densities of 3 kA/cm2 and efficiencies of 0.066 W/A.

Low threshold current continuous-wave GaInNAs/GaAs VCSELs

Vertical cavity surface-emitting lasers (VCSELs) emitting near 0.85 /spl mu/m are becoming increasingly important for short-haul optical fiber transmission systems. These devices benefit from highly reflective and thermally conductive all-epitaxial GaAs-based mirrors and efficient transverse confinement through AlAs-oxide dielectric apertures. Extending this commercially-established technology to wavelengths in the 1.3-1.6 /spl mu/m range allows for dramatically increased transmission bandwidth and distance in conventional single- and multi-mode fiber. GaInNAs is a promising active layer material grown on GaAs that can achieve 1.3 /spl mu/m emission, and electrically pulsed broad-area GaInNAs VCSELs have been realized. We demonstrate for the first time low-threshold (/spl sim/1 mA) GaInNAs VCSELs emitting at a wavelength of 1.2 /spl mu/m under continuous-wave room temperature operation.

Pulsed 25-108/spl deg/C operation of GaInNAs multiple quantum well vertical cavity lasers

Summary form only given.GaAs-based vertical cavity surface emitting laser (VCSEL) diodes are becoming increasingly important in transmitters. By using GaInNAs MQW active regions, the emission wavelength of GaAs-based lasers can be extended into the range of 1200-1300 nm. In addition, the reduced temperature sensitivity of this active region allows for the possibility of uncooled transmitter operation.

Room temperature continuous-wave operation of GaInNAs long wavelength VCSELs

Vertical cavity surface-emitting lasers (VCSELs) are becoming increasingly important for short-haul optical fiber transmission systems. Given the commercial success of GaAs-based 850 nm VCSELs, dramatic enhancements in transmission bandwidth and distance can be achieved in conventional single- and multi-mode fiber by extending the emission wavelength to the 1300 nm-1550 nm range. GaInNAs is a promising active layer material grown on GaAs that can achieve 1300 nm emission (Kondow et al., 1997), and electrically pulsed broad-area GaInNAs VCSELs (Larson et al., 1998; Coldren et al., 2000) have been realized. Here, we take advantage of the properties of GaAs-based materials-thermally-conductive high contrast mirrors and AlAs-oxide current apertures-to demonstrate for the first time low-threshold (/spl sim/1 mA) GaInNAs VCSELs emitting at a wavelength of 1200 nm under continuous-wave (CW) room temperature operation.