Recently, GaN has attracted much attention for short wavelength LEDs, LDs and future opto-electronic integrated devices. In our study, Boronmonophosphide(BP) grown on Si(100) by MOCVD is used for growing cubic-GaN (c-GaN). The epitaxial growth of GaN/BP/Si has been carried out. We observed the crystal defects by scanning electron microscope(SEM), transmission electron microscopy(TEM), and surface X-ray diffraction(XRD). The dislocation density in the BP layer markedly decreased with increasing the thickness. However the difference of the lattice constant between BP and Si leads to high dislocation densities in GaN layer. Therefore, the epitaxial growth of Si doped BP on Si has been carried out, in order to observe the effect of Si doping on BP crystalline quality. We observed the crystal defects by XRD and cross-sectional TEM. The dislocation of interfaces will be discussed.

The mechanism leading to RT ferromagnetism in Gd-doped GaN is not agreed upon, despite many experimental and theoretical reports. Oxygen impurities have been proposed as a possible contributor to ferromagnetic behavior in GaN:Gd films. In this report, GaN:Gd thin films grown by MOCVD using two different metalorganic Gd precursors are examined. The two precursors are (TMHD)3Gd, which contains oxygen, and Cp3Gd, which does not. The films have been characterized by XRD, VSM, and EDS. EDS measurements indicate that the TMHD3Gd samples contain oxygen, while the Cp3Gd samples do not, and VSM scans show that the TMHD3Gd samples exhibit much higher magnetic moments than the Cp3Gd samples, supporting the theory that oxygen enhances the ferromagnetic behavior of GaN:Gd.

We report the dry etch of GaSb(001) by inductively coupled plasma reactive ion etcher. Silicon Oxide, deposited by PECVD, was used as a mask. The oxide layer proved to be almost unaffected compared to the GaSb, when using chlorine compound gases as etchants (Cl2, BCl3, and SiCl4) as well as argon. This provides high selectivity for GaSb to the mask layer. The sample holder has no silicon that may contribute to the etching process. Etching using Cl2 + Ar showed increase in the etching rate as the chlorine ratio increases; however, the process led to grassy surface and chemical like reaction. The use of SiCl4+Cl2+Ar mixture with low chlorine ratio resulted in anisotropic etch with smooth sides. It has been found for this case that the increase of the chlorine ratio led to an increased etching rate as well. The repeat of previously reported result by Swaminathan et al. [Thin Solid Films 516 (2008) 8712.] yet with a sample holder not having silicon, proved the effect of Si-contribution in producing vertical profile etch with smooth surfaces.

Three types of Ganium Nitride (GaN) transistors were studied in this work. The devices were fabricated and exhibited unique characteristics over on-state current and off-state blocking performances. We also compared the performance differences of devices fabricated by multiepitaxial GaN/AlGaN layers on different substrates (Sapphire and Si) and evaluated the correlations among starting substrate, device variation, and manufacturing uniformity. The first device is a normally-on device with Sapphire substrate which shows good drain saturation current (Idsat) and breakdown characteristics, but the gate leakage current is quite large. The second device is a normally-off GaN transistor named metal-insulate-semiconductor (MIS) heterojunction field-effect transistor (MIS-HFET) which exhibits good performance with threshold voltage (Vth) of 3V and breakdown voltage (Vbd) of over 1800V. However the third device is a normally-off GaN metal-oxide-semiconductor field-elect transistor (MOSFET) structure which is rather difficult to exhibit good blocking characteristic due to inadequate doping process control of the reduce-surface-field (RESURF) region.

We report a comprehensive study of the cost of materials used in the thermoelectric module as the elements, substrate, and metal interconnect are optimized for maximum output power. The power conversion cost [$/W] is analyzed. The maximum power output is found by matching both thermal and electrical impedances to the external load and heat sink. The fractional area coverage or fill factor of the thermoelement (leg) in the module is a key factor which affects the overall cost of the waste heat recovery system. Thermal spreading resistance is a function of the thermal conductivity and the thickness of the substrates. Also the air gap between the legs contributes to parasitic heat loss from the hot to the cold substrate through heat conduction and radiative heat transfer. The optimum fill factor under atmospheric air-pressure is found to be on the order of a few percent. We also take into account the three-dimensional current flow and the effect of the metallization thickness on the series resistance in the module. Calculations identify the minimum metal trace thickness needed to have a minimum impact on output power generation.

As compound semiconductors continue to make inroads into common electronic devices, it is critically important to lower the cost of the primary metal-organic chemical vapor deposition (MOCVD) epitaxial process, which creates the foundation for the devices. Both GaN-based light-emitting diode (LED) and AsP-based concentrator photovoltaic (CPV) markets have been focused on simultaneous cost-reduction, cycle time reductions, and device efficiency improvements, which can be realized utilizing higher growth rates and operating pressures. To achieve these goals, it has become increasingly important to understand the underlying growth mechanisms that drive the chemistry within the MOCVD process.

Higher growth rates and higher operating pressures both result in parasitic gas-phase particle formation, which degrades the physical, electrical and optical properties of the deposited layers. In extreme cases, it can reduce the deposition efficiency to the point where increasing the reactant constituents results in reduced growth rates. In this paper, we will examine the tradeoffs that need to be made to achieve good crystal quality with abrupt interfaces, smooth surface morphology, and good minority carrier properties for films deposited at high growth rates and high pressure. While exceptional device performance has been achieved for both GaN-based LEDs and AsP-based CPV cells, it is primarily cost that is limiting full-scale adoption of compound semiconductors into these potentially enormous markets.

Creation of nanoscale building blocks with various sizes and shapes are critical for the progress of nanotechnology. Silicon carbide nanostructures attract interest due to their applications in optoelectronic devices, sensors, high-power/high temperature electronics, and thermoelectrics. This paper presents a detailed study of SiC nanowire morphology change through gas flow dynamics. SiC nanowire synthesis has been carried out by chemical vapor deposition using hexamethyldisilane (HMDS) as source material on SiO2/Si substrate. The study has been limited to several catalyst materials, including nickel (nanoparticle and thin film), cobalt nanoparticles, and gold thin film. The growth runs have been carried out at 1000oC under H2 as carrier gas with flow rates varying from 100 to1000 sccm. A significant change in morphology has been observed. At high flow rates, the nanowires are highly curved and contain sharp kinks, while the nanowires are straight and longer at lower flow rates. Moreover, it is important to note that the flow rate has influenced the nanowire growth-yield significantly. As small as 8nm-diameter SiC nanowire has been observed, as determined by transmission electron microscopy (TEM). These findings will help in controlling the morphology of the SiC nanowires. The fabricated nanowires have also been characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR).

In this paper we discuss the formation of InN on GaN heterostructures. Film growth was accomplished using a new method coined Migration Enhanced Epitaxial Afterglow (MEAglow), an improved form of pulsed delivery Plasma Enhanced Chemical Vapour Deposition (PECVD) [1]. Initial x-ray diffraction (XRD) analysis results indicated that an InGaN alloy layer formed under the InN during growth. No GaN was seen from the original buffer layer. It was postulated that indium metal deposited prior to complete nitridation diffused into the relatively thin GaN layer producing InGaN. To verify the integrity of the insulating GaN layer, a third party GaN substrate was substituted. Results were unchanged. Parameters were then modified to reduce the amount of indium used for the initial metal deposition. XRD results indicated a sharper interface between the semi-insulating GaN and conductive InN layer. Hall Effect measurements are included. We’ve shown that the growth of a device suitable heterostructure is possible using the MEAglow technique.

Use of aluminum alloyed zinc oxide (AZO) as a transparent contact to p-GaN has received significant attention for GaN/InGaN light emitting diodes applications. Reports show that AZO as deposited on p-GaN forms a Schottky contact given the large work-function difference between AZO and p-GaN [1]. However, utilization of a thin nickel layer inserted between the AZO and p-GaN can result in an ohmic contact [2], given that Ni forms an ohmic contact to p-GaN upon annealing. Here, we undertake simulation studies of this AZO/Ni interface as a function of Nickel layer. Simulation studies of the transport mechanism in this contact indicate the likelihood of a tunneling junction at the AZO/Ni interface, thus the entire AZO/Ni forming an ohmic contact to p-GaN. Potential to better control injected current density uniformity utilizing such a contact structure is also discussed.

Cadmium Sulphide (CdS) thin films have been prepared on ultrasonicated glass substrates using a specially designed chemical bath deposition technique via isochronal synthesis. The structural properties have been determined through XRD. The nanostructures have been identified in FE-SEM images. The chemical analysis has been carried out through EDAX. Optical analysis and PL studies were carried out on these films. The growth conditions and the characterization results exhibit strong dependence on the pH of the precursor solution as well as the temperature of the bath. Cu doping has been employed on the tailored films to make them low resistive and efficient for window layer applications.

InxGa1-xN-based LED structures were grown on digital AlxGa1-xN/GaN DBR substrate to enhance emission extraction. Same LED structure was grown on sapphire substrate as a comparison. LEDs grown on DBR substrate exhibited similar IV characteristics to that grown on sapphire substrate but emission-angle-dependent EL spectra were observed. Also, the resonant vertical cavity modes were observed in EL spectra of LEDs with DBR structure and compared to simulated results. Image processing analysis results show that light extraction of LEDs is enhanced with use of DBR substrate.

Silicon (Si) has been the dominating material platform of microelectronics over half century. Continuous technological advances in circuit design and manufacturing enable complementary metal-oxide semiconductor (CMOS) chips with increasingly high integration complexity to be fabricated in an unprecedently scale and economical manner. Conventional Si-based planar lightwave circuits (PLCs) has benefited from advanced CMOS technology but only demonstrate passive functionalities in most circumstances due to poor light emission efficiency and weak major electro-optic effects (e.g., Pockels effect, the Kerr effect and the Franz–Keldysh effect) in Si. Recently, a new hybrid III-V-on-Si integration platform has been developed, aiming to bridge the gap between Si and III-V direct-bandgap materials for active Si photonic integrated circuit applications. Since then high-performance lasers, amplifiers, photodetectors and modulators, etc. have been demonstrated. Here we review the most recent progress on hybrid Si lasers and high-speed hybrid Si modulators. The former include distributed feedback (DFB) lasers showing over 10 mW output power and up to 85 oC continuous-wave (cw) operation, compact hybrid microring lasers with cw threshold less than 4 mA and over 3 mW output power, and 4-channel hybrid Si AWG lasers with channel space of 360 GHz. Recently fabricated traveling-wave electro-absorption modulators (EAMs) and Mach-Zehnder interferometer modulators (MZM) on this platform support 50 Gb/s and 40 Gb/s data transmission with over 10 dB extinction ratio, respectively.

We report a study of InGaN and InAlN epilayers grown on GaN/Sapphire substrates by microfocused three-dimensional X-ray Reciprocal Space Mapping (RSM). The analysis of the full volume of reciprocal space, while probing samples on the microscale with a focused X-ray beam, allows us to gain uniquely valuable information about the microstructure of III-N alloy epilayers. It is found that “seed” InGaN mosaic nanocrystallites are twisted with respect to the ensemble average and strain free. This indicates that the growth of InGaN epilayers follows the Volmer-Weber mechanism with nucleation of “seeds” on strain fields generated by the a-type dislocations which are responsible for the twist of underlying GaN mosaic blocks. In the case of InAlN epilayer formation of composition gradient was observed at the beginning of the epitaxial growth.

We investigated, by employing a photoluminescence technique, the etching damage introduced in near-surface regions of GaN by Ar and Kr plasmas and clarified the differences between the damage characteristics of these regions for the two plasma etching cases. For Ar plasma, the shallow donor-acceptor pair emission at ~3.28 eV was significantly weakened; additionally, a broad blue luminescence band arose at approximately ~3.0 eV. In contrast, for Kr plasma under high gas pressure, we found the recovery of the damage to the same level as the as-grown crystallinity. These differences in the damage characteristics for the two plasma etching cases probably depend upon which atom (N or Ga) is preferentially etched in these cases.

We have focused to grow cubic GaN (c-GaN) on Si(100) substrates using boronmonophosphide (BP) buffer crystals. The growth of GaN was carried out by MOVPE on BP/Si(100) substrate of 2 inches in diameter. By the several evaluations, it was recognized that when the growth temperature is around 750˚C, c-GaN was dominant. The typical growth rate was about 0.5μm/h. We obtained c-GaN layer over 2.5μm thick without cracking.

Distributed Bragg Reflectors (DBRs) are an important component of various optoelectronic devices for ultra violet and visible wavelengths. In the III-Nitride material system, Aluminum Nitride (AlN) and Gallium Nitride (GaN) offer a large contrast in refractive index and are therefore well suited for fabricating DBRs with high reflectivity and wide bandwidths using relatively few periods. However, the large lattice and thermal mismatch leads to cracking in these heterostructures. In this work short period superlattice layers have been used to fabricate high reflectivity (> 94%) nitride based DBRs via Metal Organic Vapor Phase Epitaxy. Short period AlN/GaN superlattices containing three to four monolayers of GaN have been employed as the low refractive index layer in DBRs to minimize cracking. Using this technique, crack-free DBRs reflecting from 440-475 nm with up to 25 periods have been fabricated. The technique has been proven to be versatile and resulted in large area yield DBRs grown on a variety of different sapphire substrates.

The effects of source field plates on AlGaN/GaN High Electron Mobility Transistor reliability under off-state stress conditions were investigated using step-stress cycling. The source field plate enhanced the drain breakdown voltage from 55V to 155V and the critical voltage for off-state gate stress from 40V to 65V, relative to devices without the field plate. Transmission electron microscopy was used to examine the degradation of the gate contacts. The presence of cracking that appeared on both source and drain side of the gate edges was attributed to the inverse piezoelectric effect. In addition, a thin oxide layer was observed between the Ni gate contact and the AlGaN layer, and both Ni and oxygen had diffused into the AlGaN layer. The critical degradation voltage of AlGaN/GaN High Electron Mobility Transistors during off-state electrical stress was determined as a function of Ni/Au gate dimensions (0.1-0.17μm). Devices with different gate length and gate-drain distances were found to exhibit the onset of degradation at different source-drain biases but similar electric field strengths, showing that the degradation mechanism is primarily field-driven. The temperature dependence of sub-threshold drain current versus gate voltage at a constant drain bias voltage were used to determine the trap densities in AlGaN/GaN high electron mobility transistors (HEMTs) before and after the off-state stress. Two different trap densities were obtained for the measurements conducted at 300-493K and 493-573K, respectively.