COMPARISONS OF PHASE TIMES WITH TUNNELING TIMES BASED ON ABSORPTION PROBABILITIES

The times spent by an electron in a scattering event or tunnelling through a potential barrier are investigated using a method based on the absorption probabilities. The reflection and transmission times derived from this method are equal to the local Larmor times if the transmission and reflection probability amplitudes are complex analytic functions of the complex potential. The numerical results show that they coincide with the phase times except as the incident electron energy approaches zero or when the transmission probability is too small. If the imaginary potential covers the whole space the tunnelling times are again equal to the phase times. The results show that the tunnelling times based on absorption probabilities are the best of the various candidates.

Resonant magnetopolaron effects due to interface phonons in GaAs/AlGaAs multiple quantum well structures

Polaron cyclotron resonance (CR) has been studied in three modulation-doped GaAs/Al0.3Ga0.7As multiple quantum well structures in magnetic field up to 30 T. Large avoided-level-crossing splittings of the CR near the GaAs reststrahlen region, and smaller splittings in the region of the AlAs-like optical phonons of th AlGaAs barriers, are observed. Based on a comparison with a detailed theoretical calculation, the high frequency splitting, the magnitude of which increases with decreasing well width, is assigned to resonant polaron interactions with AlAs-like interface phonons.

A RESONANT RAMAN-STUDY ON PHONONS IN GAINAS/ALINAS MULTIPLE-QUANTUM WELLS

The LO phonon modes in the barrier layers of a GaInAs/AlInAs multiple quantum well structure are investigated by resonance Raman scattering (RRS), the excitation laser photon energy tuned to resonate with the above barrier interband transition energy. The resonance enhancement of LO phonon peaks are shown to be caused by Frohlich electron-phonon interaction. The pressure-dependent profiles for both AlAs-like (LO(2) mode) and InAs-like (LO(1) mode) Raman peak intensities are well fitted by the Gaussian lineshape. The shift between these two profiles can be explained by the outgoing RRS mechanism, providing information on the pressure-induced shift of the excitonic transition energy. The amplitude ratios of the two profiles are close to 1, showing a well defined two-mode behavior and the nearly equal polarizability for Al-As and In-As bonds in AlInAs alloy.

STUDIES ON TUNNELING ESCAPE TIME OF ELECTRONS FROM A QUANTUM-WELL IN MULTILAYERED HETEROSTRUCTURES

By considering the time variation of band-edge profile arising from the decay of injected charge in quantum wells(QWs), we employ a wave packet method to verify that the actual escape time of certain amount of electrons from QWs could be much larger than that for a single electron. The theoretical result is also in agreement with our measurement of escape time, performed by using a newly developed method--transient current response.

Laterally Electrostatically Driven Poly 3C-SiC Folded-Beam Resonant Microstructures

Micromachined comb-drive electrostatic resonators with folded-cantilever beams were designed and fabricated. A combination of Rayleigh＇s method and finite-element analysis was used to calculate the resonant frequency drift as we adjusted the device geometry and material parameters. Three micromachined lateral resonant resonators with different beam widths were fabricated. Their resonant frequencies were experimentally measured to be 64.5,147.2, and 255.5kHz, respectively, which are in good agreement with the simulated resonant frequency. It is shown that an improved frequency performance could be obtained on the poly 3C-SiC based device structural material systems with high Young＇s modulus.

A Hybrid Random Number Generator Using Single Electron Tunneling Junctions and MOS Transistors

This paper proposes a novel single electron random number generator (RNG). The generator consists of multiple tunneling junctions (MTJ) and a hybrid single electron transistor (SET)/MOS output circuit. It is an oscillator-based RNG. MTJ is used to implement a high-frequency oscillator,which uses the inherent physical randomness in tunneling events of the MTJ to achieve large frequency drift. The hybrid SET and MOS output circuit is used to amplify and buffer the output signal of the MTJ oscillator. The RNG circuit generates high-quality random digital sequences with a simple structure. The operation speed of this circuit is as high as 1GHz. The circuit also has good driven capability and low power dissipation. This novel random number generator is a promising device for future cryptographic systems and communication applications.

High power red-light GaInP/AlGaInP laser diodes with nonabsorbing windows based on Zn diffusion-induced quantum well intermixing

The layer structure of GaInP/AlGaInP quantum well laser diodes (LDs) was grown on GaAs substrate using low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique. In order to improve the catastrophic optical damage (COD) level of devices, a nonabsorbing window (NAW), which was based on Zn diffusion-induced quantum well intermixing, was fabricated near the both ends of the cavities. Zn diffusions were respectively carried out at 480, 500, 520, 540, and 580 Celsius degree for 20 minutes. The largest energy blue shift of 189.1 meV was observed in the window regions at 580 Celsius degree. When the blue shift was 24.7 meV at 480 Celsius degree, the COD power for the window LD was 86.7% higher than the conventional LD.

High-Power Distributed Feedback Laser Diodes Emitting at 820nm

By etching a second-order grating directly into the Al-free optical waveguide region of a ridgewaveguide（RW） AlGaInAs/AlGaAs distributed feedback（DFB） laser diode,a front facet output power of 30mW is obtained at about 820nm with a single longitudinal mode. The Al-free grating surface permits the re-growth of a high-quality cladding layer that yields excellent device performance. The threshold current of these laser diodes is 57mA,and the slope efficiency is about 0.32mW/mA.

A New Method to Investigate InGaAsP Single-Photon Avalanche Diodes Using a Digital Sampling Oscilloscope

A near-infrared single-photon detection system is established by using pigtailed InGaAs/InP avalanche photodiodes. With a 50GHz digital sampling oscilloscope, the function and process of gated-mode (Geiger-mode) single-photon detection are intuitionally demonstrated for the first time. The performance of the detector as a gated-mode single-photon counter at wavelengths of 1310 and 1550nm is investigated. At the operation temperature of 203K,a quantum efficiency of 52% with a dark count probability per gate of 2. 4 * 10~(-3), and a gate pulse repetition rate of 50kHz are obtained at 1550nm. The corresponding parameters are 43% , 8. 5 * 10~(-3), and 200kHz at 238K.

Temperature Distribution in Ridge Structure InGaN Laser Diodes and Its Influence on Device Characteristics

Time-dependent thermal simulation of ridge-geometry InGaN laser diodes is carried out with a two-dimensional model. A high temperature in the waveguide layer and a large temperature step between the regions under and outside the ridge are generated due to the poor thermal conductivity of the sapphire substrate and the large threshold current and voltage. The temperature step is thought to have a strong influence on the characteristics of the laser diodes. Time-resolved measurements of light-current curves,spectra, and the far-field pattern of the InGaN laser diodes under pulsed operation are performed. The results show that the thermal lensing effect improves the confinement of the higher order modes and leads to a lower threshold current and a higher slope efficiency of the device while the high temperature in the active layer results in a drastic decrease in the slope efficiency.

Resonant Raman Scattering and Photoluminescence Emissions from Above Bandgap Levels in Dilute GaAsN Alloy

The transitions of E0 ,E0 ＋A0, and E＋ in dilute GaAs（1-x） Nx alloys with x = 0.10% ,0.22% ,0.36% ,and 0.62% are observed by micro-photoluminescence. Resonant Raman scattering results further confirm that they are from the intrinsic emissions in the studied dilute GaAsN alloys rather than some localized exciton emissions in the GaAsN alloys. The results show that the nitrogen-induced E E＋ and E0 ＋ A0 transitions in GaAsN alloys intersect at a nitrogen content of about 0.16%. It is demonstrated that a small amount of isoelectronic doping combined with micro-photoluminescence allows direct observation of above band gap transitions that are not usually accessible in photoluminescence.