50mm 3C-SiC epilayers are grown on (100) and (111) Si substrates in a newly developed horizontal low-pressure hot-wall CVD reactor under different growth pressures and flow rates of H2 carrier gas.The structure,electrical properties,and thickness uniformity of the 3C-SiC epilayers are investigated by X-ray diffraction (XRD),sheet resistance measurement,and spectroscopic ellipsometry.XRD patterns show that the 3C-SiC films have excellent crystallinity.The narrowest full widths at half maximum of the SiC(200) and (111) peaks are 0.41° and 0.21°,respectively.The best electrical uniformity of the 50mm 3C-SiC films obtained by sheet resistance measurement is 2.15%.A σ/mean value of ±5.7% in thickness uniformity is obtained.

N-wells are created by P+ ion implantation into Si-faced p-type 4H-SiC epilayer.Ti and Ni are deposited in sequence on the surface of the active regions.Ni2Si is identified as the dominant phase by X-ray diffraction (XRD) analysis after metallization annealing.An amorphous C film at the Ni2Si/SiC interface is confirmed by an X-ray energy-dispersive spectrometer (XEDS).The Ni2Si and amorphous C film are etched away selectively,followed by deposition of new metal films without annealing.Measurement of the current-voltage characteristics shows that the contacts are still ohmic after the Ni2Si and amorphous C film are replaced by new metal films.The sheet resistance Rsh of the implanted layers decreases from 975 to 438Ω/□,because carbon vacancies (VC) appeared during annealing,which act as donors for electrons in SiC.

4H-SiC MESFETs are fabricated on semi-insulating SiC substrates.Key processes are optimized to obtain better device performance.A microwave power amplifier is demonstrated from a 1mm SiC MESFET for S band operation.When operated at a drain voltage of 64V,the amplifier shows an output power of 4.09W,a gain of 9.3dB,and a power added efficiency of 31.3%.

Partially-depleted silicon-on-insulator(PDSOI)floating-body(FB)nMOSFETs and H-gate type body-contacted(BC)nMOSFETs are fabricated with different back channel implantation dosages.The off-state breakdown characteristics of these devices are presented.The off-state breakdown voltages of the FB nMOSFETs increase from 5.2 to 6.7V,and those of the H-gate type BC nMOSFETs decrease from 11.9 to 9V as the back channel implantation dosages increase from 1.0e13 to 1.3e13cm-2.By measuring the parasitic bipolar transistor static gain and the breakdown characteristics of the pn junction between the drain and the body,the differences between the breakdown mechanisms of the FB and H-gate type BC nMOSFETs are analyzed and explained qualitatively.

Thick GaN films were grown on GaN/sapphire template in a vertical HVPE reactor.Various material characterization techniques,including AFM,SEM,XRD,RBS/Channeling,CL,PL,and XPS,were used to characterize these GaN epitaxial films.It was found that stepped/terraced structures appeared on the film surface,which were indicative of a nearly step-flow mode of growth for the HVPE GaN despite the high growth rate.A few hexagonal pits appeared on the surface,which have strong light emission.After being etched in molten KOH,the wavy steps disappeared and hexagonal pits with {1010} facets appeared on the surface.An EPD of only 8e6cm-2 shows that the GaN film has few dislocations.Both XRD and RBS channeling indicate the high quality of the GaN thick films.Sharp band-edge emission with a full width at half maximum(FWHM)of 67meV was observed,while the yellow and infrared emissions were also found.These emissions are likely caused by native defects and C and O impurities.

A single power supply common-gate (CG) current mode transimpedance preamplifier (TIA) is developed with a 0.5μm GaAs PHEMT process.The amplifier has a measured -3dB bandwidth of 7.5GHz and a transimpedance gain of 45dBΩ.Both the input and output voltage standing wave ratios (VSWR) are less than 2 within the bandwidth.The equivalent input noise current spectral density varies from 14.3 to 22pA/Hz,with an average value of 17.2pA/Hz.Having a timing jitter of 14ps and eye amplitude of about 138mV,the measured output eye diagram for 10Gb/s NRZ pseudorandom binary sequence (PRBS) is clear and satisfactory.

Improved waveguide designs for 9.0μm GaAs-based quantum cascade laser (QCL) structures are presented.Modal losses and confinement factors are calculated for TM modes with the transfer matrix method (TMM) and effective index method (EIM).The thicknesses of the cladding layer and waveguide layer,the ridge-width,and the cavity length are all taken into account.Appropriate thicknesses of epilayers are given with lower threshold gain and more economical material growth time.

A new approach for the design and implementation of a programmable voltage reference based on an improved current mode bandgap voltage reference is presented.The circuit is simulated and fabricated with Chartered 0.35μm mixed-signal technology.Measurements demonstrate that the temperature coefficient is ±363ppm/℃ from 0 to 100℃ when the VID inputs are 11110.As the supply voltage is varied from 2.7 to 5V,the voltage reference varies by about 5mV.The maximum glitch of the transient response is about 20mV at 125kHz.Depending on the state of the five VID inputs,an output voltage between 1.1 and 1.85V is programmed in increments of 25mV.

An effective method is introduced to investigate the strained fields and piezoelectric effect in GaN/AlN quantum dots (QDs) with hexagonal truncated pyramid shape.The strain distribution and charge density were calculated using the finite element method (FEM).It is shown that spontaneous and piezoelectric polarization resulted in the separation of electrons and holes,bringing about a strong built-in electric field in the QD structures.The strain field and piezoelectric potential influence the distribution of charges.The electrons are localized near the top of the QDs,and the holes are localized in the wetting layer just below the pyramid.Furthermore,the piezoelectric potential in the QDs affects the electron levels and band edge shape.

Low energy helium ion implantation into InP heterostructures that induces controlled quantum well intermixing is reported and used for the first time.A significant blue-shift enhanced by a moderate RTA process is achieved.An intermixed FP laser is fabricated.Compared to the unimplanted laser,the lasing wavelength of the intermixed laser blue-shifts by 37nm.

The effects of high temperature treatment by conventional furnace annealing and rapid thermal processing (RTP) on the dissolution and the re-growth behavior of oxygen precipitation in Czochralski (CZ) silicon wafers are investigated.It is found that RTP is a rapid and effective way to dissolve oxygen precipitation in comparison with conventional furnace annealing.After dissolution treatment by RTP,the density of bulk micro-defects (BMDs) increases remarkably during the subsequent anneal for the re-growth of oxygen precipitation,while after dissolution treatment by conventional furnace annealing,the density of BMDs is nearly unchanged during the subsequent annealing for the re-growth of oxygen precipitation.The higher the subsequent annealing temperature,the faster the re-growth of oxygen precipitation in silicon wafers subjected to the dissolution treatment.

ZnO nanowires were synthesized without any kind of catalyst on a-plane sapphire substrate by chemical vapor deposition (CVD).Only the (100) and (101) diffraction peaks of ZnO were found on the XRD patterns of the samples.SEM images show that the ZnO nanowires are parallel to the sapphire substrate.Following the deposition of Au finger electrodes on the samples, the samples’ UV-sensitive performance was detected with a wavelength of illumination of 256nm. The results show that the ZnO nanowires respond very fast to UV-light, the ratio of photo current to dark current is about 30 at 5V, and the maximum photo-responsibility is of 0.56 A/W at 354nm.

Influences of different porosities in SiC powder source on as-grown crystal are investigated.The temperature distributions in the powder and growth chamber are analyzed for powder sources with different porosities.Combining these results with growth experiments,the relation between the isothermal line and the surface shape of as-grown crystal is also discussed.All simulated and experimental results indicate that the crystal surface shape is determined directly by isothermality in the growth chamber,and that more porosity in the powder is propitious to the evaporation of powder and crystal growth.

The magnetic viscosity of Si melt under a magnetic field (REC) is investigated with the oscillation cup method.The results show that the magnetic viscosity of Si melt increases with the increase of the magnetic field strength.The relation between the magnetic viscosity and magnetic field strength can be expressed by the formula,η=η0+aB2.This is the research foundation for MCZSi.

To enhance the coupling strength between the gate and the quantum dot (QD) confined in the transport channel and improve the gain modulation factor,we develop a novel type of Si single-electron transistor (SET).Clear coulomb blockade oscillations and negative differential conductance (NDC) are observed at room temperature (RT).Based on the model of quantized energy levels of QDs,we analyze the transport mechanism of the fabricated devices,especially the effect of strong gate-dot coupling on the transport characteristics.The results demonstrate that 7.6nm QDs and a large gain modulation factor of 0.84 by controlling the thermal oxidation are achieved.

Due to the geometry and polarization of AlGaN/GaN HEMTs, the electric field in the gate-drain region is very high, and is sufficient to produce a tunneling current from the gate metal to the surface of the AlGaN barrier layer. The electrons that tunnel to the semiconductor surface can accumulate on the surface near the gate, resulting in the extension of the depletion region and current collapse. Bias stress measurements were made to determine an AlGaN/GaN HEMT's current collapse. Surface passivation prevents the electrons from getting trapped at the surface, and a field plate suppresses the electric field at the gate edge, thereby reducing the gate leakage by a significant factor. Thus the current collapse can be effectively suppressed by surface passivation and the field-plate structure.

Changes in the typical electronic parameters of SiGe HBTs irradiated by pulse neutron and gamma rays from a reactor are measured.The DC common emitter static current gain of the SiGe HBTs only decreases by about 20% after being irradiated with 1e13cm-2 neutron fluence and 256.85Gy(Si) gamma total dose.The base current and the junction leakage current increase,while the collector current and the breakdown voltage decrease for SiGe HBTs after radiation.After irradiation,the cutoff frequency fT is nearly unchanged,but the maximum oscillation frequency fmax decreases a little.The mechanisms of the reactor pulse neutron and gamma rays irradiation damage for SiGe HBTs are preliminarily analyzed.

By analyzing resonant tunneling transistors (RTTs) synthesized with different device structures and treating RTTs with different device structures as inverter circuits,a unified inverter model for RTTs is established.In this model,the I-V characteristics of an RTT can be derived and analyzed with the same method used to analyze an inverter.The various I-V characteristics of RTTs with different device structures can then be explained with a unified inverter theory.The results derived by this model are in agreement with those of corresponding circuit simulations and experiments.This unified inverter model of RTTs is a powerful tool for the design and analysis of RTTs.

Plasma-induced damage on 90nm Cu dual Damascene technology devices is investigated.Experiments on the hot carrier stress for nMOSFETs and NBTI stress for pMOSFETs are conducted.The antenna ratio is still a standard for detecting plasma-induced damage.The via structure shows more plasma damage than other metal structures.This is explained by the via first dual Damascene process.

High-efficiency n-nc-Si∶H/p-c-Si heterojunction solar cells are fabricated by hot-wire chemical vapor deposition (HWCVD) at low temperatures.The effects of the crystalline fraction of nc-Si∶H,especially in the buffer layer,and hydrogen treatment time on the performance of the solar cells are investigated.The interface between nc-Si∶H and c-Si is examined by HRTEM.The influence of hydrogen dilution of the buffer layer on the structure of the interface is analyzed.By optimizing the deposition parameters,an nc-Si∶H/c-Si heterojunction solar cell with Jsc=40.8mA/cm2,Voc=576.3mV,FF=73.75%,and η=17.36% has been achieved on CZ single crystalline silicon.

An Al0.6Ga0.4As/AlAs distributed Bragg reflector (DBR) for a 630nm peak wavelength high brightness AlGaInP LED is studied.The reflective characteristics of normal DBR and coupled DBR are simulated using the interference matrix model.The simulated DBR structures and corresponding LEDs are grown by LP-MOCVD.The simulated and experimental results both indicate that the coupled DBR can remarkably increase the light extraction efficiency of an AlGaInP LED.The non-encapsulated LED with the coupled DBR performs well,with 2.3mW output optical power,12 lm/W luminous efficiency,and 5.6% external quantum efficiency,with an improvement of 35% over that with a normal DBR.

High efficiency output of a violet LED is obtained by increasing the growth temperature of InGaN quantum wells,reducing the intermingling efficiency of In content,and improving the quality of InGaN/GaN.High-resolution X-ray double crystal diffraction and a scanning tube microscope are used to characterize the configuration and optical characteristics of InGaN/GaN MQW grown at high temperatures.The output power of a packaged 300μm×300μm LED is 5.2mW under a 20mA input current,the output wavelength is 408nm.

High-power ridge-waveguide tapered diode lasers at 14xx nm are designed theoretically.InGaAsP/InP-based diode lasers with compressively strained quantum wells and wavelengths around 14xx nm are grown by MOCVD.Cavity-spoiling grooves are etched down through the active region to prevent a direct feedback path between the front and rear facets outside of the ridge region.Lasers with a total length L=1900μm and different ridge waveguide lengths LRW are processed to study the influence of the straight section on the spatial mode filtering.The devices have optimized characteristic parameters and excellent beam quality when the ridge waveguide length is 700μm and the output power is 1.21W.Lasers with LRW=700μm and different taper lengths L taper are also processed to study the influence of the taper section on Ith,Es,Pmax,and the spatial mode filtering.The optimized devices have better characteristic parameters and excellent beam quality with a taper length of 1000μm.

Three novel MEMS microneedles are designed and fabricated.Aiming at practical applications,the mechanical characteristics of the microneedles and process of fluid flowing through the microchannels are studied through both theoretical analysis and numerical simulation with the finite element method.The results show that the microneedles designed here are strong enough to guarantee safe injection through skin,and they are suitable for delivering drugs in micro-volumes.

A novel MOEMS tunable filter is proposed. We choose GaAs/AlGaAs as the bottom distributed Bragg reflector (DBR),GaAs and SiO2/Si as the top DBR,and air as the cavity. Parameters of the device,such as the FWHM,transmittance,tuning deflection,and tuning velocity,are analyzed theoretically according to the demand of the WDM system. The influences of the depth h,width b,and length L on tuning deflection and tuning velocity are investigated in detail. The tuning deflection increases with the increase of L and decreases with the increase of h and b,while the tuning velocity behaves in the opposite way.

Surface damage on InGaAs,n-InP,and p-InP after Ar+ etching is studied,and it is removed by wet etching post treatments.After Ar+ etching,the root-mean-square roughness of InGaAs surface is lower,but the roughness of n-InP and p-InP surfaces is significantly higher.The photoluminescence (PL) intensity of Ar+-etched InGaAs increases,but those of Ar+-etched n-InP and p-InP decreases.X-ray photoelectron spectroscopy (XPS) is used to investigate the atomic concentration of three samples before Ar+ etching and after Ar+ etching and wet etching post treatments.After Ar+ etching,the content of In and Ga at the InGaAs surface increases markedly,and there is generally a preferential loss of P from n-InP and p-InP surfaces.The surface atomic concentration of the samples after wet etching is almost the same as before Ar+ etching.

The "zone method" is introduced to simulate wall temperature distribution in an MOCVD reactor.This method is used to calculate the wall temperature distribution of a radial flow MOCVD reactor with three separate vertical inlets.Results show that the distribution rule for the wall temperature differs at different walls.When the radial flow MOCVD reactor with three separate vertical inlets is put in a natural convective heat transfer environment,the maximum difference in wall temperature is 123K.Such a temperature difference will have large effects on gas flow behavior and the deposition process.In order to keep the walls at low temperatures,the outer convective heat transfer coefficient must be larger than 84W/m2·K.

A new RF-MOSFET model for low voltage low power (LVLP) CMOS RFIC CAD application is presented.This model is developed based on the EKVv2.6 model.The gate oxide overlap resistances and the losses of the substrate are cleverly considered.Equivalent circuits biased at zero and linear regions are used to extract all the radio-frequency parasitic parameters analytically.The model is finally used to model an 8-gate-finger (channel mask length L=0.24μm,finger width W=9.58μm) n-MOSFET,which was fabricated in a 0.25μm RF-CMOS process supplied by CSM (Chartered Semiconductor Manufacture Ltd).Comparison of simulated and measured DC data at S-parameters of up to 40GHz demonstrates the excellent accuracy of the model.

A classical double exponential expression of a transient current pulse in a single event effect is confirmed by numerical optimization of results from 3D device numerical simulation.An equation that gives the relationship between transistor bias voltage and transient current is derived by theoretical analysis.This equation can be used to simulate the SEU of an SRAM cell in the circuit simulation tool HSPICE.Finally,the critical LET of an SRAM cell is obtained by circuit simulation and mix-mode simulation.The practicability of this method is verified by comparing the precision and time cost.