A mode for the periodicity and weakening surge in semi-insulating GaAs photoconductive semiconductor switches is proposed based on the transferred-electron effect.It is shown that the periodicity and weakening surge is caused by the interaction between the self-excitation of the resonant circuit and transferred electron oscillation of the switch.The bias electric field (larger than Gunn threshold) across the switch is modulated by the AC electric field,when the instantaneous bias electric field E is swinging below Gunn electric field threshold ET but greater than the sustaining field ES (the minimum electric field required to support the domain) at the time of the domain reaching the anode,and then the delayed-dipole domain mode of switch is obtained.It is the photon-activated carriers that satisfy the requirement of charge domain formation on carrier concentration and device length product of 1e12cm-2,and the semi-insulating GaAs photoconductive semiconductor switch is essentially a type of photon-activated charge domain device.

A monolithic voltage controlled oscillator (VCO) based on negative resistance principle is presented utilizing commercially available InGaP/GaAs hetero-junction bipolar transistor (HBT) technology.This VCO is designed for 5GHz-band wireless applications.Except for bypass and decoupled capacitors,no external component is needed for real application.Its measured output frequency range is from 4.17 to 4.56GHz,which is very close to the simulation one.And the phase noise at an offset frequency of 1MHz is -112dBc/Hz.The VCO core dissipates 15.5mW from a 3.3V supply,and the output power ranges from 0 to 2dBm.To compare with other oscillators,the figure of merit is calculated,which is about -173.2dBc/Hz.Meanwhile,the principle and design method of negative resistance oscillator are also discussed.

A three-stage MMIC power amplifier operating from 6 to 18GHz is fabricated using 0.25μm AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT).The amplifier is fully monolithic,with all matching,biasing,and DC block circuitry included on the chip.The power amplifier has an average power gain of 19dB over 6～18GHz.At operation frequencies from 6 to 18GHz,the output power is above 33.3dBm,and the maximum output power of the MMIC is 34.7dBm at 10GHz.The input return loss is less than -10dB and the output return is less than -6dB over operating frequency.This power amplifier has,to our knowledge,the best power gain flatness reported at C-X-Ku-band applications.

This paper introduces a novel digital transceiver for the cordless telephone zero (CT0) standard,which uses a digital modulation and demodulation technique to handle the signal instead of the traditional analog method.In the transmitter,a fractional-N phase locked loop (PLL) is utilized to realize the continuous phase frequency shift key (CPFSK) modulation,and a 2 Ts raised cosine (2RC) shaping technique is used to reduce the occupied bandwidth.In the receiver,a novel digital method is proposed to demodulate the 2RC CPFSK signal.This chip is fabricated using an SMIC 0.35μm mixed signal CMOS process with a die size of 2mm×2mm.With an external low noise amplifier (LNA),the sensitivity of the chip is better than -103dBm.

A novel approximation of the two-dimensional (2D) potential function perpendicular to the channel is proposed,and then an analytical threshold voltage model for a fully depleted SOI-MOSFET with a non-uniform Gaussian distribution doping profile is given based on this approximation.The model agrees well with numerical simulation by MEDICI.The result represents a new way and some reference points in analyzing and controlling the threshold voltage of non-uniform fully depleted (FD) SOI devices in practice.

A modified LLP variational method is adopted to discuss the polaronic effect on the binding energy of an impurity in an infinite quantum well by considering the pressure and screening effects.The influences from three optical phonon modes in the system (including confined longitudinal optical (LO) phonons,half-space LO phonons,and interface optical phonons) on the binding energy are considered.The results show that the polaronic effect significantly decreases the binding energy,but pressure weakens the polaronic effect.The influence of screening on the polaronic effect is not apparent.

GaAs/AlGaAs (110) multiple quantum wells (MQWs) were grown by solid source molecular beam epitaxy (MBE) with a valved arsenic cracker cell. The optical properties of the undoped GaAs (110) MQWs were studied by low-temperature photoluminescence and time-resolved photoluminescence (TRPL), which show that a strong electron spin relaxation dynamic is dependent on the excitation power and wavelength at room temperature. In this material, the predominant spin scattering mechanism ［D'yakonov-Perel' (DP) mechanism］ for conventional (100) QWs is substantially suppressed. The experiment data indicate that the electron-hole exchange interaction has a great impact on the spin relaxation time in GaAs (110) MQWs at room temperature.

The band gaps of ternary zinc blende BxIn1-xP and BxGa1-xP alloys are calculated using first principles in the generalized gradient approximation (GGA),and their bowing parameters are obtained.For BxIn1-xP,the bowing parameters are b_Eg(Γ)=4.32eV and b_Eg(X)=1.8eV,the crossover composition from direct to indirect gap is 0.47,the direct gap varies from 1.33 to 1.47eV,and the addition of a small amount of B will reduce the alloy gap.For BxGa1-xP,the whole x range is indirect gap,and the bowing parameters are b_Eg(Γ)=1.37eV and b_Eg(X)=2.46eV.The reason that BxIn1-xP and BxGa1-xP have relatively large bowing parameters is the large lattice mismatch between their binary alloys.

The effect of annealing atmosphere on the behavior of oxygen precipitates and their induced defects in Czochralski silicon during high temperature annealing is investigated.The silicon wafers were subjected to a low-high two-step annealing followed by a high-temperature annealing in five different atmospheres.It was found that the amount of dissolved oxygen precipitates in the high temperature annealing is independent of the annealing atmospheres,whereas the annealing atmospheres influence the distribution of the bulk micro-defects (BMDs) in the cross section of the wafers.It was confirmed that the high-temperature annenaling in various atmospheres induced different point defects in the wafer and thus affected the distribution of BMDs.This investigation could be beneficial for the selection of annealing atmosphere in the internal gettering process during the manufacture of the integrated circuits.

The transport,kinetics,and growth process of ZnO single crystal fabricated by the chemical vapor transport method (CVT) are studied through analyzing the effect of temperature gradient and calculating the transport efficiency.The factors which limit growth rate and crystal quality are discussed within the framework of the theories of vapor-solid phase crystallization and growth kinetics.Finally,we identify the CVT growth mechanism of ZnO,which is supported by our experimental results of high quality,large ZnO single crystals.

A model for the built-in electric field in the base is developed and calculated analytically.The model is suitable for a base with a Gaussian doping distribution and different Ge profiles (e.g.,triangle,box-triangle).A new formula for the valence band effective states is obtained,and the effect of the conduction band effective states on the built-in electric field is considered for the first time.It is found that the effect of the Ge fraction on the built-in electric field is larger than that of impurities.When the Ge fraction profile is triangular,the built-in electric field increases gradually from emission to collector with the total Ge fraction.At a given location x,the built-in electric field becomes larger and larger with the increasing of the total Ge fraction.When the Ge fraction profile is box-triangular,the built-in electric field increases from emission junction to collector for a given x1 and a given Ge fraction yc.For an invariable Ge fraction profile,the built-in electric field is nearly invariable.For a linearly graded Ge fraction profile,the built-in electric field becomes larger and larger with the increasing of x1.In addition,there is a sharp drop near x1.

The persistent photoconductivity effect in unintentionally doped n-GaN grown by metal organic chemical vapor deposition (MOCVD) is presented.The photoconductivity build-up and its decay behavior with different excitation intensities and different wavelength ranges are observed.The experiment shows persistent photocurrent (PPC),negative photocurrent (NPC),and negative persistent photocurrent (NPPC) trends as the excitation intensity is changed from low to high when the excitation light includes wavelengths larger than the absorption edge of GaN.It is believed that the phenomenon is ruled by competition between capture and release photo-generated electrons and holes by deep electron traps and deep hole traps,respectively.

Tin-doped indium oxide (ITO) thin films were deposited on glass substrates by reactive thermal evaporation.The effect of the preferred orientation of ITO thin film on its performance has been studied.The results show that the grain orientation in the (400) direction does not influence the transmissivity and the carrier concentration,but enhances the carrier mobility.The transmissivity of ITO films is over 90% in the visible wavelength region (except for film deposited at 125℃).To deposit (222)- and (400)-oriented ITO films on the same thin film Si/single crystalline Si solar cells separately,the photoelectric conversion efficiency is 10.31% and 12.92%,respectively.This result indicates that the (400) preferred orientation of ITO film can improve the efficiency of solar cells.The optimal substrate temperature and oxygen flow are 225℃ and 4sccm,respectively.Under this condition,the resistivity of ITO film is 4.8e-4Ω·cm,and the figure of merit reaches 3.8e-2 □/Ω.

ZnO:Dy3+ nanocrystals have been synthesized by solid state reaction.X-ray diffraction (XRD),transmission electron microscopy (TEM),and selected area electronic diffraction (SAED) demonstrate that the nanocrystals can be indexed as hexagonal wurtzite polycrystalline.The photoluminescence spectra (PL) and photoluminescence excitation spectra (PLE) of the nanocrystals were measured at room temperature.The grain size of the nanocrystals is about 50nm as calculated using the Debye-Scherrer formula.We have found that in the PL of ZnO:Dy3+ nanocrystals,besides sharp lines from the 4f→4f transition of Dy3+,two broad bands appear from the Dy defects A and B in ZnO,with peaks at 600 and 760nm and full widths at half maximum (FWHM) of about 200 and 100nm,respectively.Under the exciton excitation (385nm),the intensity of the peak at 760nm is far stronger than that of the peak at 600nm.The relative intensity of each peak in the emission spectrum depends on the excitation wavelength and the concentration of the Dy3+.Under the excited state of Dy3+ (454nm),the emission of broad bands with peaks at 600 and 760nm is lost.Only the 4f→4f transitions of Dy3+ remain.

A self-consistent solution that simultaneously satisfies the Schrodinger equations and Poisson equation is used to calculate the band structure and gain spectra of InGaN/AlInGaN,InGaN/GaN,InGaN/InGaN,and InGaN/AlGaN.It is found that the polarized electrons on the interface of the heterostructure are the main factor limiting the optical gain.The intensity of the spontaneous emission spectrum can be improved if AlInGaN,which can reduce the number of polarized electrons,is used as a barrier.Considering the effect of the polarized electrons and the barrier energy gap,a method is put forward to optimize the proportion of every element in the AlInGaN barrier,and physical explanations are given.

PbI2 single crystal,an important room temperature radiation material,was grown using a special technique,and a detector sensitive to γ-ray was also fabricated.XRD analysis indicates that the structure of the grown crystal is 2H with hexagonal space group of P3m1.IR measurement shows that the transmission rate of the crystal sample (10mm×10mm×1mm) reaches 40% on average in the range of 400～4000cm-1.UV absorption testing indicates that the cut-off wavelength of the sample is 547.6nm,corresponding to a band gap of 2.27eV.A room temperature detector fabricated from the grown crystal is sensitive to 241Am 59.5keV γ-rays.The full width at half maximum (FWHM) of the obtained energy spectrum is 26.7keV.

Growth of GaN film by HVPE was carried out on MOCVD-GaN template and sapphire substrate.The surface of GaN film grown on GaN template was flat and bright,but cracked heavily.The FWHM for GaN (0002) DCXRD is at least 141" .The quality of samples grown directly on sapphire substrate was poor,with a FWHM 1688" for GaN (0002),but it did not crack at all.The carrier gas flow rate was found to have a great effect on pre-reactions.Stress was produced at the interface between the epitaxial layer and the substrate.Holes at the interface can relax the stress greatly,which is helpful for reducing cracks.The yellow luminescence in the PL spectrum arose from O impurity.

GaN thin films with mixed-polarity were initially grown on (0001) sapphire substrates by molecular beam epitaxy (MBE).The samples were etched by alkali solution,and porous GaN films were formed.GaN thick films were grown on the porous GaN layers by hydride vapor phase epitaxy (HVPE).These HVPE-GaN epilayers were characterized by atomic force microscopy,X-ray diffraction,and photoluminescence spectroscopy.The results indicate that the crystalline quality of HVPE-GaN is improved by using the porous GaN buffer,as the stress is reduced markedly.

Quartz is widely used as the wall of MOCVD reactors.We compared numerical simulations performed by six different models of the quartz emissivity,transmissivity and reflectivity.The models include the transparent-body model,a black body model,a gray body model,a three-band specular reflective model,a three-band diffusive reflective model,and a two-band model.These models are combined with the zone method to simulate wall temperature distribution in the MOCVD reactor with three separate vertical inlets.Results show that the temperature distributions of a quartz wall are largely influenced by the wall properties,in which the wall emissivity is the largest,and the wall transmissivity is the smallest.The rule of wall temperature distributions differs for different walls.

A new structure is presented for designing and fabricating a static induction transistor (SIT).The transistor is designed to be surrounded by a deep groove to cut off the various probable parasitic effects that may degrade the device performance,especially the parallel-current effect.A mathematical model for the parasitic effect of SIT is proposed and simulated with PSPICE.The simulation results agree with the experiments.The novel structure is effective for avoiding the parallel-current effect.The etching technique of the groove is also investigated in depth in this paper.

The characteristics,experiment,and three dimensional device simulations of a new planar split dual gate (PSDG) MOSFET device are reported for the first time.Theoretical calculation and 3D simulation as well as the experimental data show that the two independent split dual gates can provide dynamical control of device characteristics such as threshold voltage and sub-threshold swing as well as the device saturated current.The PSDG MOSFET transistor leakage current can be reduced by as much as 78% of a traditional single gate MOSFET.The PSDG is fabricated and fully compatible with our conventional 0.18μm logic process flow.

Fundamental equations for an RSD are derived through semiconductor theory.By considering the high level injection and high electric field effects,a physical model of an RSD is constructed,in which the reverse injection process is under pnn+ diode operation and the forward conduction process is under pin diode operation.Through the limit difference method,the partial differential equation of the semiconductor device is transformed into a difference equation,and the corresponding boundary condition is discretized with high accuracy.Combined with a typical RSD circuit,the circuit equations are written,and the voltage-time and current-time waveforms are gotten by means of the Runge-Kutta algorithm and the non-equilibrium carrier distribution.By comparing an RSD discharge experiment and model computation,the difference between the theoretical results and the experimental results are analyzed.The practical value of the model and algorithm is shown through an application circuit.As a result,the physical model and the numerical algorithm are proved valid,which lead a predictive role for RSD device design and circuit simulation.

The relation between the maximum temperature and the switching condition of an LDMOST under different frequencies is studied.The results show that the maximum temperature in the device depends on the thermal capacitance,the power dissipation,the duty cycle,and the duration of continuous operation under a high switching frequency.Under a low switching frequency,the maximum temperature depends not only on those four parameters,but also on the thermal resistance and the period of the cycle.The results given here can be used as a reference for designing the thermal safe operation conditions of power devices.

A composite collector structure containing InGaAsP was designed,which can effectively eliminate the energy spike at the B-C junction and avoid the current blocking effect.The dependence of the characteristics of a DHBT on the parameters of the collector structure were analyzed theoretically,and an optimized result was delivered which can give a theoretical direction and reference for the design of this kind of composite collector.The data were analyzed based on the theory of this paper,and a satisfactory result was obtained.

A 326～365nm AlxGa1-xN/GaN heterojunction pin photodetector is designed.Energy band diagrams of this structure with complete polarization and partial polarization and without polarization are obtained by self-consistent Schrodinger-Poisson calculation.Meanwhile,the photoelectric response spectrum of the photodetector is simulated.Using the energy band diagram and photoelectric response spectrum,the influence of the interface polarization effects on the photoelectric response of the photodetector is analyzed.

A novel method for enhancing the sensitivity and speed of CMOS optoelectronic integrated receivers called pre-equalization,which compensates the transferred signal at the input port of a preamplifier,is put forward.Based on 0.35μm CMOS technology,three types of pre-equalized optoelectronic integrated receivers are designed by parallel resonant loop peaking technique,third-order ladder network peaking technique,and high-pass filter peaking technique,respectively,where a fingered dual-photodiode is applied with a 40μm×40μm area,a 1.1GHz 3dB bandwidth,and a 0.95pF junction capacitance.The simulation results indicate that the sensitivity and speed of a receiver can be enhanced effectively by adding a third-order ladder network pre-equalization circuit,which achieves a -14dBm sensitivity and a 2GHz 3dB bandwidth with a bit error rate of 1e-12.

The influence of background radiation on a medium-wave HgCdTe photoconductive detector with an overlap structure is studied.In the experiment design,two methods are put forward to change the background radiation.It is found that the detector noise decreases with the decrease of the background radiation.The g-r noise is calculated from the number of carriers and lifetime theory.It is shown that the calculation result has the same trend as the experimentally observed phenomena.Further noise spectrum measurement shows that 1/f noise is the primary factor that causes the detector noise to change with background radiation.The edge contacts’ asymmetrical MIS structure increases the effect of background radiation on the 1/f noise.

An X-band low noise amplifier (LNA) module is designed and manufactured successfully,and an effective method for adjusting the gain flatness of the module is presented.The method entails placing several parallel resonant circuits between two low noise amplifier chips,providing different resonant frequency points at lower frequencies outside of the working band.It reduces the gain of the lower frequencies of the working band.The gain compression can be controlled by resistors added in the resonant circuits.As a result,flat gain is obtained using this method.This X-band LNA module shows a gain flatness of less than ±0.34dB,a noise figure less than 1.84dB,and a gain higher than 35dB.

This paper presents a high-resolution hybrid digital pulse wide modulation (DPWM) design which can be used in DC-DC digital controllers.This design combines the designs based on an oscillator and a counter.The design of this paper has been taped out based on the process of Chartered 0.35μm 2P4M CMOS.The test results of the chip indicate that it can generate 4-phase output at the frequency of 950kHz while maintaining its 11bit resolution.Each phase has a phase difference of 90°.

A low power,high PSRR voltage reference with an amplifier and a novel self-bias active load is proposed.The low frequency PSRR of the voltage reference and the open-loop gain of the self-bias active load amplifier are discussed.The proposed voltage reference is implemented in an XFAB XB06 process.The nominal output is 1.206V,the supply current is 6mA,the temperature coefficient is 40ppm/℃,and the low frequency PSRR is 85dB.

A new method for the real-time measurement of junction temperature is introduced.For transistors dissipating power at a constant rate,the heating current is treated as the measuring current in order to measure directly the junction temperature of the transistors.The method can be used in on-line measurements.

The high temperature characteristics of the ohmic contact of Ti/Al/Ni/Au (15nm/220nm/40nm/50nm) multilayer contacts to n-type GaN(Nd=3.7e17cm-3,Nd=3.0e18cm-3) are studied.The annealed samples still show excellent ohmic contact characteristics at 500℃.Contact resistivity increases with the rise of temperature.Furthermore,the tendency of increase is related to doping concentration:The higher the doping concentration,the slower the increase of the contact resistivity with the temperature.Ti/Al/Ni/Au ohmic contact to heavy doping n-GaN has better high temperature reliability.The contact resistivity shows unrecoverable characteristics after the samples are placed under the thermal stress.

We investigate the effects of the configurations of the chamber and the coil of an inductively coupled plasma (ICP) etcher and the process parameters on the homogeneity of plasma distribution.Using the modules of plasma,electromagnetic field,etc.in the commercial software CFD-ACE+,a two-dimensional discharge model of an ICP etcher was built.The spatial distributions of the electron temperature Te and the electron number density ne of argon plasma were simulated at 10mTorr,200W,and 200sccm.One-dimensional distribution profiles of the plasma parameters above the wafer's surface at different pressures and powers were compared.These results demonstrate that ne increases with both pressure and power,and Te decreases with pressure,and decreases at first but then increases with power in a lesser range.A shielding slab can be used to enhance the plasma density through analyzing its effect on plasma parameters.Furthermore,the results show that Te increases but ne decreases with the porosity of the shielding slab.

The three dimensional temperature distribution of laser bonding with a Gaussian thermal source is modeled using the finite element method.In the model,the temperature distribution with different process parameters is simulated and the bondline width is obtained.Then the key process parameters of laser bonding,including laser power,scanning velocity,and initial temperature,are obtained with the help of scanning experiments.Finally,with regression analysis on the simulation results,a regression model is made and the optimal process parameters of laser bonding are found.This can provide a theoretical basis for further study on laser bonding.