K. X. Chen

Effect of dislocations on electrical and optical properties of n-type Al0.34Ga0.66N

The effect of edge and screw dislocations on the electrical and optical properties of n-type Al0.34Ga0.66N is investigated. It is found that edge dislocations strongly affect the electrical properties of n-type Al0.34Ga0.66N. Both free carrier concentration and mobility decrease with increasing edge dislocation density. Edge dislocations also enhance nonradiative recombination, which is indicated by decreasing near-band-edge UV as well as parasitic blue photoluminescence. The UV/blue ratio is found to be independent of the edge dislocation density but strongly depends on the Si doping concentration.The effect of edge and screw dislocations on the electrical and optical properties of n-type Al0.34Ga0.66N is investigated. It is found that edge dislocations strongly affect the electrical properties of n-type Al0.34Ga0.66N. Both free carrier concentration and mobility decrease with increasing edge dislocation density. Edge dislocations also enhance nonradiative recombination, which is indicated by decreasing near-band-edge UV as well as parasitic blue photoluminescence. The UV/blue ratio is found to be independent of the edge dislocation density but strongly depends on the Si doping concentration.

High‐frequency response of capacitors fabricated from fine grain BaTiO3 thin films

Fine grain BaTiO3 thin films with a grain size ranging between 100 and 1000 A were deposited using the reactive partially ionized beam deposition technique at 550–600 °C. A metal/insulator/metal structure of these materials was fabricated and the dielectric response was measured up to 40 GHz using a network analyzer. It is shown that these films are not ferroelectric. However, these films show a dielectric relaxation in the frequency interval between several MHz and 1 GHz. We propose that this indicates a relaxation mechanism not related to the ferroelectric domain walls.

Recombination dynamics in ultraviolet light-emitting diodes with Si-doped AlxGa1−xN∕AlyGa1−yN multiple quantum well active regions

Ultraviolet (UV) light-emitting diodes with AlxGa1−xN∕AlyGa1−yN multiple quantum well active regions, doped in the barriers with different Si doping levels, show a sharp near-band edge emission line (UV luminescence). Some samples have a broad subband gap emission band centered at about 500 nm (green luminescence) in addition to the near-band edge emission. The electroluminescence intensities of the UV and green emission line are studied as a function of the injection current. For the sample grown on the AlN substrate under optimized growth conditions, the UV luminescence intensity increases linearly with the injection current, following a power law with an exponent of 1.0, while the green luminescence intensity increases sublinearly with the injection current. On the contrary, the samples grown on the sapphire substrate show a superlinear (to the power of 2.0) and linear (to the power of 1.0) dependence on the injection current for the UV and green luminescence, respectively. A theoretical model is propo...

Parasitic sub-band-gap emission originating from compensating native defects in Si doped AlGaN

The authors investigate the dependence of the photoluminescence intensity ratio between the near-band-edge and the parasitic blue emission as a function of silane flow in n-type Al0.3Ga0.7N. It is found that when the silane flow rate is higher than 1.13×10−9mol∕min, the UV-to-blue ratio is a constant. When the silane flow rate is lower than 1.13×10−9mol∕min, the UV-to-blue ratio increases rapidly as the silane flow rate decreases. A theoretical model is proposed, which assumes that the parasitic blue emission is caused by an acceptorlike compensating native defect. The model is fully consistent with the experimental results.

Study of electron trapping in the amorphous tantalum oxide thin films prepared by d.c. magnetron reactive sputtering

Abstract Amorphous tantalum pentoxide (Ta2O5) thin films on n-type Si substrates were prepared by d.c. magnetron reactive sputtering deposition technique. It was observed that the leakage current decreased with time when a voltage bias was first applied. The cause of this behavior was investigated using bias-temperature-stress test technique combined with the capacitance-voltage measurement with structures of Al/Ta2O5/Si metal-oxide-semiconductor (MOS) capacitors, and was identified to be owing to electron trapping in the Ta2O5 film and at the Ta2O5/Si interfaces. The current injection technique was further used to correlate the amount of charge trapped in the Ta2O5 with the leakage current passed through the Ta2O5 film, and it was found that most of the trapped electrons were located at the Ta2O5/Si interface. This electron trapping effect on the conduction mechanisms of the Ta2O5 films and the related reliability issues in dynamic random access memories applications are discussed.

The temperature-composition phase diagram and the miscibility gap of Hg 1−x Cd x Te solid solutions by dynamic mass-loss measurements

The dynamic mass-loss technique has been employed to measure Hg partial pressures over Te-saturated Hg1-xCdxTe solid solutions with x = 0.40, 0.54, and 0.70 in the 10-1 to 10-4 atm range. The relative chemical potentials of HgTe in Hg1-xCdxTe solid solutions have been calculated using the measured Hg partial pressures at temperatures below 413°C, and fitted into an analytical expression. A Gibbs-Duhem integration yielded the relative chemical potentials of CdTe. By combining the relative chemical potentials of the binary components HgTe and CdTe, an expression for the Gibbs free energy of mixing was derived. The binodal (miscibility gap) and spinodal curves of the Hg1-xCdxTe solid solutions have been established with the critical temperature and composition of 221°C and Hg0.40Cd0.60Te.

Observation of phase separation in Hg 1−x Cd x Te solid solutions by low incident angle x-ray diffraction

The low incident angle (surface analysis) and the conventional wide angle (bulk analysis) x-ray diffraction techniques were employed to investigate the existence of a miscibility gap in the Hg1−xCdxTe system. Samples of initial composition Hg0.46Cd0.54Te were annealed at 140 and 400°C, respectively, for four weeks. The diffraction planes (531) and (642) have been selected for the x-ray diffraction analysis. The results of this work provide the first, direct experimental evidence for the existence of a miscibility gap at lower temperature in the Hg1−xCdxTe system. The phase separation occurs primarily in a thin surface layer at 140°C and is reversible after annealing at 530°C. The compositions of the two compounds at the tie-line at 140°C are Hg0.22Cd0.78Te and Hg0.63Cd0.37Te.

Kinetic study of Al-mole fraction in AlxGa1−xN grown on c-plane sapphire and AlN bulk substrates by metal-organic vapor-phase epitaxy

A systematic study is performed on the dependence of the Al-mole fraction in AlxGa1−xN on the organometallic group-III precursor flow during metal-organic vapor-phase epitaxy. When keeping the total organometallic volume flow constant, a nonlinear concave bowing relationship is found between the Al-mole fraction (for 0⩽x⩽1) and the relative trimethylaluminum volume flow. A kinetic model, which takes into account the growth rate ratio between GaN and AlN (gGaN∕gAlN), is developed to explain such concave bowing relationship. The experimental data are in excellent agreement with the theoretical model. For AlxGa1−xN growth on AlN bulk substrates, it is found that the Al-mole fraction is smaller and the growth rate ratio is larger than on sapphire substrates. The authors also investigate the incorporation of Al in AlxGa1−xN as a function of the group-III precursor molar flow rate. A positive convex bowing relationship is found between Al-mole fraction and the relative trimethylaluminum molar flow, which is con...