H. Temkin

Electron beam induced current measurements of minority carrier diffusion length in gallium nitride

Minority carrier diffusion length in epitaxial GaN layers was measured as a function of majority carrier concentration and temperature. The diffusion length of holes in n‐type GaN is found to decrease from 3.4 to 1.2 μm in the doping range of 5×1015–2×1018 cm−3. The experimental results can be fitted by assuming the Einstein relation and by the experimental dependence of hole mobilities on carrier concentration. The low injection carrier lifetime of ∼15 ns, used in the fit, is largely independent of the doping level. The diffusion length, measured for ∼5×1015 and 2×1018 cm−3 dopant concentrations, shows an increase with increasing temperature, characterized by an activation energy Ea of ∼90 meV, independent of the impurity concentration.

High quality GaN–InGaN heterostructures grown on (111) silicon substrates

We report on the low pressure metal organic chemical vapor deposition of single crystal, wurtzitic layers of GaN and GaN/InGaN heterostructures on (111) GaAs/Si composite substrates. The structural, optical, and electrical properties of the epitaxial layers are evaluated using x‐ray diffraction, transmission electron microscopy, photoluminescence, and measurements of minority carrier diffusion length. These measurements demonstrate high quality of GaN grown on the composite substrate.

Cleaved cavity optically pumped InGaN–GaN laser grown on spinel substrates

We report an optically pumped multiple‐quantum‐well laser of InGaN–GaN grown on cubic, (111)‐oriented spinel substrates. The laser cavity is formed by cleaving. Atomic force microscopy shows that the cleaved GaN and spinel facets are of similar flatness. The onset of lasing is clearly demonstrated by the saturation of spontaneous emission, abrupt line narrowing, and the highly polarized light output. A lasing threshold power of 140 kW/cm2 is measured in a 400‐μm‐long cavity at 150 K.

Polarization instability and relative intensity noise in vertical‐cavity surface‐emitting lasers

We observe a polarization instability in circularly symmetric vertical‐cavity surface‐emitting lasers. A relatively long time, 3–5 ns, is required to establish a dominant polarization state. Under high‐speed digital modulation this leads to strong enhancement, 20–30 dB, in polarization resolved low‐frequency relative intensity noise. This polarization instability is accurately described by a simple rate‐equation model. A similar increase in relative intensity noise, under dc bias, is caused by energy partition between orthogonally polarized modes.

Kinetics of thermal oxidation of AlAs in water vapor

We have investigated the lateral thermal oxidation of AlAs in water vapor in vertical cavity surface emitting laser structures. At low temperatures and short oxidation times, oxide growth was found to be reaction rate limited. Conversely, diffusion across the oxide was the rate controlling mechanism at higher temperatures and longer oxidation times. Lasers are typically processed at intermediate values of temperatures and time. The observed growth can be modeled by rate equations by which the two component growth mechanisms can be separated. Activation energies of 1.6 and 0.8 eV were determined for the reaction rate and diffusion limited mechanisms, respectively.

Strained quaternary quantum well lasers for high temperature operation

We describe compressively strained separate confinement heterostructure 1.3 μm quantum well lasers optimized for high temperature operation. The active layer consists of ten GaInAsP wells, each 40–80 A thick, grown under compressive lattice mismatch strain of Δa/a≤0.75%. Within the constraints of the well composition and thickness imposed on the active region, strain is necessary for efficient laser operation. Best results are obtained for Δa/a∼0.2%–0.3% with the laser threshold as low as 5 mA and slope efficiency of 42 mW/mA. In the temperature range of 25–85 °C a slope efficiency change as small as 30% was achieved. Power output of at least 20 mW can be maintained up to 100 °C at a current drive below 150 mA.

InGaN‐GaN based light‐emitting diodes over (111) spinel substrates

In this letter we report the deposition of high quality GaN‐InGaN double‐heterostructure pn junctions over (111) spinel substrates using low‐pressure metalorganic chemical vapor deposition. A ten‐period undoped GaN‐In0.1Ga0.9N multiple quantum well was used for the active region. Mesa‐type light‐emitting diode (LED) structures were fabricated which under forward bias exhibited only strong band‐edge electroluminescence. The spectral emission was centered at 385 nm and had a linewidth of 15 nm. This is similar to what is measured for similar LED structures over sapphire substrates.

Effect of barrier recombination on the high temperature performance of quaternary multiquantum well lasers

We use spectrally resolved measurements of spontaneous emission to investigate the temperature characteristics of strained and lattice matched InGaAsP multiquantum well lasers. Carrier overflow into the barriers and separate confinement layers and the resulting recombination are demonstrated to be an important factor limiting high temperature performances in these devices. The barrier recombination does not saturate above threshold, instead it increases with the drive current. This effect is further enhanced with increased temperature. We show that the reduction in the barrier recombination correlates quantitatively with increased high temperature slope efficiency.

InGaAs-InGaAsP buried heterostructure lasers operating at 2.0 /spl mu/m

Buried heterostructure lasers with highly strained InGaAs-InGaAsP active regions, emitting at 2 /spl mu/m have been fabricated and tested. The lasers exhibited threshold current densities of 500 A/cm/sup 2/ for 1-mm-long cavities, an internal loss of 11 cm/sup -1/, and characteristic temperatures as high as 50/spl deg/C. The gain characteristics were also investigated and a linewidth enhancement factor of 8 was determined.<<ETX>>

Spontaneous emission factor and its scaling in vertical cavity surface emitting lasers

We report room‐temperature measurements of the spontaneous emission factor β in high‐quality gain‐guided GaAs/AlGaAs vertical cavity surface emitting lasers. In devices with 6‐μm diameter we obtain β=2.8×10−3. The measured scaling of β with the cavity volume agrees well with classical electromagnetic model of dipole radiation. The magnitude of β exceeds that predicted by classical theory by approximately a factor of 2.