S. Z. Wang

Pulsed photothermal reflectance measurement of the thermal conductivity of sputtered aluminum nitride thin films

We report on measurements of the thermal conductivity of reactively sputtered aluminum nitride (AlN) thin films with different thickness, ranging from 100nm to 1μm, on silicon substrates. The measurements were made at room temperature using the pulsed photothermal reflectance technique. The thermal conductivities of the sample are found to be significantly lower than the single-crystal bulk AlN and increase with an increasing thickness. The thermal resistance at the interface between the AlN film and the silicon substrate is found to be about 7–8×10−8m2K∕W.

Rapid thermal annealing of GaNxAs1−x grown by radio-frequency plasma assisted molecular beam epitaxy and its effect on photoluminescence

The effect of rapid thermal annealing (RTA) on GaNAs films grown on GaAs (100) substrates by radio frequency plasma-assisted solid source molecular beam epitaxy was investigated by low-temperature photoluminescence (PL) and high-resolution x-ray diffraction (HR-XRD) measurements. GaNAs samples with N content of 1.3% and 2.2% determined by experimental curve fitting of x-ray rocking curve with the dynamical diffraction theory, exhibit an overall blueshift in energy of 67.7 meV and an intermediate redshift of 42.2 meV in the PL spectra when subjected to RTA at 525–850 °C for 10 min. The results suggest that the GaNAs layer may have undergone an intermediate substitutional–interstitial diffusion in addition to purely outdiffusion of nitrogen atoms. Samples annealed at 700–750 °C showed 1.7–2.1 times improvement in integrated PL intensity and 1.6–1.8 times reduction in PL full width half maximum as compared to the as-grown sample. The HR-XRD results show no significant changes in GaNAs lattice parameter betwe...

Physical mechanisms of photoluminescence of chlorine-doped ZnSe epilayers grown by molecular beam epitaxy

Reported here are some temperature-dependent and excitation-dependent photoluminescence (PL) results from chlorine-doped ZnSe layers grown by molecular beam epitaxy. The PL spectrum is characterized by an overwhelming exciton recombination emission at 2.797 eV (10 K) near the band edge, and no other PL features are found. This overwhelming neutral donor-bound exciton (Cl0X) emission line at 2.797 eV (10 K) with a full width at half maximum (FWHM) of ∼13 meV reveals the high crystalline quality of the samples. The quick quenching of this exciton line above 200 K is due to the presence of a nonradiative center with a thermal activation energy of ∼90 meV. The decrease of the Cl0X line over the temperature range from 10 to 200 K is due to the thermal activation of Cl0X bound excitons to free excitons with an activation energy of ∼9.0 meV. The change of the emission nature occurs at about ∼200 K from Cl0X bound exciton recombination to free exciton recombination; accordingly, a kink appears on the temperature-...

Photoluminescence characteristics of GaInNAs quantum wells annealed at high temperature

The photoluminescence (PL) characteristics of GaInNAs quantum wells (QWs) after high-temperature postgrowth annealing were studied. The QWs were grown using a radio-frequency nitrogen plasma source in conjunction with a solid-source molecular-beam epitaxy system. It was found that annealing at high temperature (840 °C) and long duration (10 min) results in significant improvements to the PL characteristics of the GaInNAs QWs. The shift of the GaInNAs and GaInAs PL peak wavelength resulting from high-temperature annealing is dependent on the In composition. It is suggested that the dominant mechanisms that give rise to the blueshift of the PL peak wavelength in GaInNAs QWs with high-In composition are residual-strain-induced GaAs/GaInNAs/GaAs interface interdiffusion, and defect-assisted diffusion-related effects, both of which originate from the growth process.

Temperature-dependent photoluminescence of GaInP/AlGaInP multiple quantum well laser structure grown by metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine

A GaInP/AlGaInP multiple quantum well laser structure was grown by low-pressure metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine. Laser diodes fabricated from this structure lased at room temperature. Photoluminescence (PL) measurements were performed from 10 to 230 K. The PL energy increased with temperature from 10 to 70 K and decreased above 70 K. The former was attributed to thermal activation of trapped carriers due to localization in the quantum wells, while the latter was attributed to temperature-induced band-gap shrinkage. The PL intensity as a function of temperature was fitted by employing two nonradiative recombination mechanisms with good agreement, resulting in two activation energies that correspond to losses of photogenerated carriers to nonradiative centers.

Transverse electric dominant intersubband absorption in Si-doped GaInAsN∕GaAs quantum wells

We report observation of transverse electric (TE) dominant intersubband absorption in Si-doped GaInAsN∕GaAs multiple-quantum-well structures. The TE dominant absorption is believed to be caused by the incorporation of nitrogen and the associated nitrogen state. When the confinement is strong in narrow quantum wells, the ground state is pushed up, which enhances the interaction with nitrogen state and significantly changes the nature of the state.

Effects of thermal annealing on deep-level defects and minority-carrier electron diffusion length in Be-doped InGaAsN

We report the effects of ex situ thermal annealing on the deep-level defects and the minority-carrier electron diffusion length in Be-doped, p-type In0.03Ga0.97As0.99N0.01 grown by solid source molecular-beam epitaxy. Deep-level transient spectroscopy measurements reveal two majority-carrier hole traps, HT1 (0.18 eV) and HT4 (0.59 eV), and two minority-carrier electron traps, ET1 (0.09 eV) and ET3 (0.41 eV), in the as-grown sample. For the sample with postgrowth thermal annealing, the overall deep-level defect-concentration is decreased. Two hole traps, HT2 (0.39 eV) and HT3 (0.41 eV), and one electron trap, ET2 (0.19 eV), are observed. We found that the minority-carrier electron diffusion length increases by ∼30% and the leakage current of the InGaAsN∕GaAsp-n junction decreases by 2–3 orders after thermal annealing. An increase of the net acceptor concentration after annealing is also observed and can be explained by a recently proposed three-center-complex model.

20 meV-deep donor level in InN film of 0.76 eV band gap grown by plasma-assisted nitrogen source

We report the photoluminescence (PL) properties of InN epilayers grown by solid-source molecular beam epitaxy on (0001) sapphire substrates with AlN buffer layers. The reactive nitrogen species were generated by a plasma-assisted radio frequency activated nitrogen plasma source. Hall measurements showed the electron concentration in unintentionally doped InN epilayers at room temperature to be around 5×1018 cm−3. Room temperature PL measurements revealed a strong emission peak at 0.76 eV with no signals detected within an energy range from 1.81 to 2.16 eV, suggesting a band gap of around 0.76 eV. The PL spectrum at 10 K showed a main emission peak at 0.74 eV and shoulder peak at 0.72 eV, with a 20 meV interval. Temperature-dependent PL measurements indicated a 20 meV-deep donor level in the InN epilayers.

The role of nitrogen-nitrogen pairs in the deviation of the GaAsN lattice parameter from Vegard’s law

We propose several physical mechanisms that may account for the difference between the nitrogen composition in GaAsN materials measured by secondary ion mass spectroscopy and x-ray diffraction. A simplified model proposed here proves that Vegard’s law remains valid as long as all nitrogen atoms in the GaAsN alloys are located substitutionally at the arsenic sites. The theoretical results based on N-N pair defects are in good agreement with the experimental data, suggesting that the N-N pairs are the predominant nitrogen-related defects that cause deviation from the GaAsN lattice constant predicted by Vegard’s law.

Fabrication of high-performance InGaAsN ridge waveguide lasers with pulsed anodic oxidation

We have demonstrated high-performance InGaAsN triple-quantum-well ridge waveguide (RWG) lasers fabricated using pulsed anodic oxidation. The lowest threshold current density of 675 A/cm/sup 2/ was obtained from a P-side-down bonded InGaAsN laser, with cavity length of 1600 /spl mu/m and contact ridge width of 10 /spl mu/m. The emission wavelength is 1295.1 nm. The transparency current density from a batch of unbonded InGaAsN RWG lasers was 397 A/cm/sup 2/ (equivalent to 132 A/cm/sup 2/ per well). High characteristic temperature of 138 K was also achieved from the bonded 10/spl times/1600-/spl mu/m/sup 2/ InGaAsN laser.