Dynamic spectral width of an InGaAsP/InP electroabsorption light modulator under high-frequency large-signal modulation

The first measurements of dynamic spectra of an InGaAsP/InP electroabsorption light modulator under high-frequency large-signal modulation are reported. A spectral broadening factor ? was determined from the relative sideband strength to the carrier, and it decreased with increasing operating electric field in the modulator. The estimated ?-value for full modulation was |?| = 2.3, which can be reduced by designing a modulator to give a more effective change of electro-absorption.     

High-speed long-wavelength optical modulation in InGaAs/InAlAs multiple quantum wells

A long-wavelength optical modulator has been fabricated which makes use of an electroabsorption effect in multiple quantum wells (MQWs). Here, InGaAs/InAlAs MQWs are prepared in a PIN configuration using molecular beam epitaxy (MBE). The rise time of the detected pulse modulation signal has been measured at 190 ps. This response level has been attributed to the detecting system response and RC time constant, and not to such intrinsic effects as carrier lifetime.     

Carrier transport in porous silicon

Carrier transport in porous silicon layers has been studied by the time-of-flight method in the strong injection mode at temperatures T=290–350 K and electric field strengths F=(1.5–7)×10⁴ V cm^?1. The electron and hole drift mobilities μ_e≈2×10^?3 cm² V^?1 s^?1 and μ_h≈6×10^?4 cm² V^?1 s^?1 were obtained at T=292 K and F=4×10⁴ V cm^?1. An exponential temperature dependence of drift mobility with activation energy of ～0.38 and ～0.41 eV for, respectively, electrons and holes was established. It is shown that the type of time dependences of the photocurrent associated with carrier drift and the superlinear dependence of the transit time on the reciprocal of the voltage applied to a sample allow use of the concept of space-charge-limited currents under the conditions of anomalous dispersive transport. The experimental data are accounted for in terms of the model of transport controlled by carrier trapping into localized states with energy distribution near the conduction and valence band edges described by an exponential function with a characteristic energy of ～0.03 eV.     

High-speed large-signal digital modulation of three-terminallow-threshold strained InGaAs/GaAs lasers

We present large-signal digital modulation of very low-threshold strained InGaAs/GaAs single quantum well (SQW) lasers with monolithically integrated intracavity modulators. The voltage controlled intracavity modulator was driven from a simple emitter-follower using a single NPN transistor. Modulation response mas obtained from dc to 1 Gbit/s with a modulation efficiency of 27% and modulation depth of nearly 100%. A bit-error-rate (BER) lower than 10^-11 was measured at 1 Gbit/s with an input signal swing of only 110 mV. We demonstrate the suitability of these devices for ultrabroad-band optical interconnection applications     

Carrier transport in laser heterostructures

We present two-dimensional numerical simulation of carrier transport in laser structures, which allows calculation of the efficiency of injected carrier consumption by the active region and the dependence of the laser current on applied voltage. It also allows calculation of the current, carrier, and potential distribution in a laser structure. This was done by use of PADRE, a program developed for the modeling of heterostructure electronic devices, which was supplemented with additional calculations of the laser optical properties. We applied this program to investigate the effect on the laser quantum efficiency of thermionic emission of electrons from the active layer. The temperature and current dependence of the laser internal quantum efficiency has been analyzed. This study allowed us to understand the performance of lasers with nearly ideal current-blocking structures     

Low-frequency operation of avalanche diodes under large-signal conditions

Application of basic Read theory to the operation of avalanche diodes at frequencies of fractions of the transit frequency is found to predict high-efficiency oscillations when a waveform consisting of a low-amplitude fundamental and a larger second harmonic in the appropriate phase is applied. The resultant-circuit current is such that the power output is essentially at the fundamental frequency.     

Theory of large-signal direct modulation of extended cavitysemiconductor lasers with dispersive loss

We present a model of coupled semiconductor diode-dispersive extended cavity lasers that describes arbitrarily large current modulation, does not assume uniform photon and carrier densities within the semiconductor diode gain medium, and is simple to implement numerically. In particular, we look at the fiber grating laser, an example of such a coupled system that has been studied as a possible optical communications source. We find simple expressions for the instantaneous frequency and intensity in terms of a few parameters characterizing the dispersion, allowing for the design of the system to minimize chirp. From these expressions we also recover Kazarinov and Henry's adiabatic chirp formula in the limit of slow modulation and Petermann's dynamical chirp formula in the limit of uniform carrier and photon densities. We show that in typical cases, where nonuniformity is important, the instantaneous frequency modulation is quantitatively and qualitatively different than is predicted by previous models     

Carrier transport across heterojunction interfaces

A general theory is presented to describe the carrier transport across heterojunction interfaces. In matching the boundary conditions at the interface, the conservation of total energy and perpendicular momentum is assumed and the difference of effective masses on two sides of the junction is taken into account. The quantum mechanical transmission coefficient is calculated by a combined numerical and WKB method. Application of the present model to an Al_xGa_1?xAsGaAs N-n heterojunction is performed and it gives rise to rectifying characteristics together with non-saturated reverse current. Comparison with the classical thermionic emission model is made to show the significance of tunneling and effect of quantum mechanical reflection.     

Carrier transport in HEMT's analyzed by high-fieldelectroluminescence

The high-field emission of visible light from GaAs and InGaAs high electron mobility transistors (HEMTs) has been used to analyze the hot-electron conduction processes in these devices. Spectral analysis of this electroluminescence has indicated that emission has several components, due to recombination in different layers of the transistor. Analysis of the luminescence provides insights into the vertical distribution of electrons and holes when the transistor is operated at high biases. From the measurements, it seems clear that hot conduction electrons flow both in the conducting channel as well as in the barriers and neighboring quantum wells, and that this dominates the electrical behavior at high drain-source bias voltages     

Darlington feedback amplifier with good bias stability under large-signal conditions

A Darlington cell using resistive biasing suffers from bias stability under large-signal conditions, which can be detrimental at radio frequencies. Replacing the resistor with a transistor in a configuration similar to a current source but acting also as an amplifier has shown a beneficial improvement.     

Carrier transport effects in active and passive modelocking of monolithic quantum-well lasers at millimeter-wave frequencies

We investigate the effect of carrier transport on active and passive resonantly enhanced modulation of monolithic quantum-well semiconductor lasers. While the ultimate frequency at which narrow-band resonant modulation can be achieved may be severely affected by carrier transport, no such limitation is predicted for passive model coupling.     

Carrier transport in semiconductor detectors of magnetic domains

Carrier transport in Hall-type devices detecting magnetic domains is analyzed in terms of a two-dimensional numerical model, using a finite element scheme. The numerical model allows the calculation of magnetic sensitivity for general device geometries or structures, any homogeneous semiconductor material, and arbitrary domain shapes and sizes. We specifically consider three types of commonly used Hall detectors: the conventional Hall plate, the split-electrode Hall device, and the Hall cross. The magnetic sensitivity for these devices is computed for various domain configurations. In particular, the device's output response for moving domains is investigated and appropriate figures of merit are established with respect to spatial resolution. A comparison of the numerical solutions with previously reported experimental results supports the validity of our analysis.     

Carrier transport and related phenomena in MOS devices

Silicon-based devices are currently the most attractive group because they are functioning at room temperature and can be easily integrated into conventional silicon microelectronics. There are many models and simulation programs available to compute CV curves with quantum correction [Choi C-H, Wu Y, Goo JS, Yu Z, Dutton RW. IEEE Trans on Electron Devi 2000; 47(10): 1843; Croci S, Plossu C, Burignat S. J Mater Sci Mater Electron 2003; 14: 311; Soliman L, Duval E, Benzohra M, Lheurette E, Ketata K, Ketata M. Mater Sci Semicond Process 2001; 4: 163]. This work deals with the simulation of electron transfer through SiO₂ barrier of metal–oxide–semiconductor structure (MOS). The carrier density is given by a self consistent resolution of Schrödinger and Poisson equations and then the MOS capacitance is deduced and compared with results available in literature. As it is well known, the MOS capacitance–voltage profiling provides a simple determination of structure parameters. The extracted tunnel oxide thickness and substrate doping are compared with those used in the simulation. For the purpose to investigate the electron tunnelling through the barrier, we have used the transfer matrix approach. Using I–V simulations, we have shown that the traps in SiO₂ matrix have a drastic influence on electron tunnelling through the barrier. The trap-assisted contribution to the tunnelling current is included in many models [Maserjian J, Zamani N. J Appl Phys 1982; 53(1): 559; Houssa M, Stesmans A, Heyns MM. Semicond Sci Technol 2001; 16: 427; Aziz A, Kassmi K, Kassmi Ka, Olivie F. Semicond Sci Technol 2004; 19: 877; Wu You-Lin, Lin Shi-Tin. IEEE Trans Dev Mater Reliab 2006; 6(1): 75; Larcher L. IEEE Trans Electron Dev 2003; 50(5): 1246]; this is the basis for the interpretation of stress induced leakage current (SILC) and breakdown events. Memory effect becomes typical for this structure. We have studied the I–V dependence with trap parameters.     

Carrier transport mechanisms in semiconductor nanostructures and devices

Semiconductor nanostructures have gained importance due to their potential application in future nanoelectronic devices. For such applications, it is extremely important to understand the electrical properties of semiconductor nanostructures. This review presents an overview of techniques to measure the electrical properties of individual and clusters of semiconductor nanostructures using microcopy based techniques or by fabricating metallic electrical contacts using lithography. Then it is shown that current–voltage (I–V) characteristics can be used to determine the conduction mechanism in these nanostructures. It has been explained that various material parameters can be extracted from I–V characteristics. The frequently observed conduction mechanism in these nanostructures such as thermally activated conduction, space charge limited current (SCLC), hopping conduction, Poole Frenkel conduction, Schottky emission and Fowler Nordheim (FN) tunneling are explained in detail.     

Carrier transport mechanisms in high-power InGaAs-InGaAsP-InGaPstrained quantum-well lasers

The mechanisms of carrier capture and escape in a high-power strained quantum-well (QW) InGaAs-InGaAsP-InGaP laser diode have been studied by CW optical spectroscopy. From the temperature dependence of the photocurrent, we deduce that the thermal escape of light holes is the mechanism limiting the carrier escape rate. By measuring the ratio of the electroluminescence signals generated from the confinement layers and the QW's, we show that the onset of a steady state of carrier capture in the QW's is determined by the limitation of the carrier mean free path by inelastic scattering events. Our findings are consistent with the record-high CW output powers reported for 0.97-μm emitting laser diodes     

Pulse-shape effects on frequency chirping in single-frequency semiconductor lasers under current modulation

Directly modulated semiconductor lasers exhibit dynamic frequency shifts (chirping) due to gain-induced variations of the refractive index. Using the small-signal analysis of the single-mode rate equations, the effect of current-pulse shape on frequency chirping is analyzed, and the results are compared for the cases of sinusoidal and square-wave modulations. The chirp is generally larger for the square-wave case. However, its magnitude depends on the pulse rise and fall times, decreasing for a pulse with slower turn-on and turn-off characteristics. Chirp analysis presented here includes the effect of power-dependent gain changes arising from the processes such as spectral hole-burning.     

Theoretical and experimental studies of the effects of compressiveand tensile strain on the performance of InP-InGaAs multiquantum-welllasers

The authors have studied, both theoretically and experimentally, the effects of biaxial strain upon the performance characteristics of broad-area InP-InGaAsP-In_xGa_1-xAs (0.33⩽x ⩽0.73) separate confinement heterostructure multiquantum-well lasers. The theoretical calculations include the effects of strain on the bandstructure and the Auger recombination rates. A pronounced dependence of the threshold current density J_th upon x is observed. The lowest measured J_th is 589 A/cm² in an 800-μm laser with x=0.68. Also, internal quantum efficiencies as high as unity and loss coefficients as low as 5.6 cm^-1 have been measured for x=0.58     

Carrier transport in the drift region of read-type diodes

The transport properties of the drift region significantly impact the conversion efficiency of Read-type IMPATT diodes. A detailed numerical study has been undertaken to gain insight into the carrier transport under large-signal conditions and the roles of depletion-width modulation and the carrier-induced electric field. A phase delay in the peak of the avalanche current results from assuming a sinusoidal voltage rather than a sinusoidal field and is incorporated in the model. induced current waveforms, transport factors, diode admittances, and conversion efficieneies are presented as functions of RF level, bias current density, and the small-signal transit angle. A region of partial collection of the drifting carriers exists between regular IMPATT operation and the onset of the premature collection mode, which provides a smooth transition between these two modes. The effects of premature collection are most pronounced at long transit angles where the corresponding large increase in the transport factor at a high RF level will give high-efficiency operation, but also a large hysteresis in the tuning characteristic. The displacement current has an appreciable effect on the induced external current under these conditions. The presented results aid the understanding of tuning behavior and tradeoffs in design for Read diodes.     

DC and large-signal time-dependent electron transport inheterostructure devices: an investigation of the heterostructure barriervaractor

The DC and large-signal time-dependent electron transport properties of Heterostructure Barrier Varactors (HBV) are investigated using a physical model which combines drift-diffusion current transport through the heterostructure bulk with thermionic and thermionic-field emission currents imposed at the abrupt heterointerfaces in a fully self-consistent manner. A fast and accurate hydrodynamic device simulator for generic unipolar InGaAs-InAlAs on InP, InGaAs-InP on InP, and GaAs-InGaAs-AlGaAs on GaAs has been developed based on this model. The experimentally observed current-voltage and capacitance-voltage characteristics of GaAs-AlGaAs and GaAs-InGaAs-AlGaAs are compared with the simulated results over a wide range of DC bias. Large-signal time-dependent simulations at a pump frequency of 100 GHz confirm the odd-harmonic operation of these devices and indicate that multiple barrier should provide efficient frequency multiplication, especially in high order frequency multipliers, broadband frequency triplers, and quasi-optical tripler arrays     

Analysis of the large-signal characteristics of powerheterojunction bipolar transistors exhibiting self-heating effects

The large-signal microwave characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) are modeled using the conventional Gummel-Poon-based bipolar junction transistor (BJT) model and extending it to include self-heating effects. The model is incorporated as a user-defined model in a commercial circuit simulator. The experimental microwave characteristics of HBTs are analyzed using the new model and harmonic balance techniques and the impact of self-heating effects on the device large-signal characteristics is investigated. Use of constant base voltage rather than constant current is more suitable for achieving maximum output power. Self-heating induced by RF drive is reduced under constant base current conditions. Increased thermal capacitance values result in gain enhancement at high power levels