The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

Gan : processing, defects, and devices

Leu-M

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

A review of Ga2O3 materials, processing, and devices

One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, position-controlled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

/pdf/one-dimensional-zno-nanostructures-solution-growth-and-30xs4d6be7.pdf

One-dimensional ZnO nanostructures: Solution growth and functional properties

Over the past two decades, several advances have been made in micromachined sensors and actuators. As the field of microelectromechanical systems (MEMS) has advanced, a clear need for the integration of materials other than silicon and its compounds into micromachined transducers has emerged. Piezoelectric materials are high energy density materials that scale very favorably upon miniaturization and that has led to an ever-growing interest in piezoelectric films for MEMS applications. At this time, piezoelectric aluminum-nitride-based film bulk acoustic resonators (FBAR) have already been successfully commercialized. Future innovations and improvements in inertial sensors for navigation, high-frequency crystal oscillators and filters for wireless applications, microactuators for RF applications, chip-scale chemical analysis systems and countless other applications hinge upon the successful miniaturization of components and integration of piezoelectrics and metals into these systems. In this article, a comprehensive review of micromachined piezoelectric transducer technology will be presented. Piezoelectric materials in bulk and thin film forms will be reviewed and fabrication techniques for the integration of these materials for microsensor applications will be presented. Recent advances in various piezoelectric microsensors will be presented through specific examples. This review will conclude with a critical assessment of the future trends and promise of this technology.

https://iopscience.iop.org/article/10.1088/0957-0233/20/9/092001/pdf

Piezoelectric MEMS sensors: state-of-the-art and perspectives

Hydrogen is readily incorporated into GaN and related alloys during wet and dry etching, chemical vapor deposition of dielectric overlayers, boiling in water, and other process steps, in addition to its effects during metalorganic chemical vapor deposition or metalorganic molecular beam epitaxial growth. The hydrogen is bound at defects or impurities and passivates their electrical activity. Reactivation of passivated shallow donors in the nitrides occurs at 450-550°C, but evolution from the crystal requires much higher temperatures (≥800°C for GaN).

The incorporation of hydrogen into III–V nitrides during processing

In a method of making a GaAs-based semiconductor laser, a fully processed wafer is cleaved, typically in the ambient atmosphere, into laser bars, the laser bars are loaded into an evacuable deposition chamber (preferably an ECR CVD chamber) and exposed to a H 2 S plasma. Following the exposure, the cleavage facets are coated in the chamber with a protective dielectric (preferably silicon nitride) layer. The method can be practiced with high through-put, and can yield lasers (e.g., 980 nm pump lasers for optical fiber amplifiers) capable of operation at high power.

Method of making a GaAs-based laser comprising a facet coating with gas phase sulphur

InGaP is found to etch in HCl, Br2MeOH or HNO3. The etch rates in HCl and Br2MeOH are faster for p-type InGaP relative to n-type material, and more rapid in In-rich samples compared to stoichiometric InGaP. Etching in 1% Br2MeOH is diffusion-limited with an activation energy of ∼4.4 kcal mol−1. Only HCl-based solutions are found to provide selective etching of InGaP over GaAs.

Investigation of wet etching solutions for In0.5Ga0.5P

InGaAs and InP exposed to N 2 or Ar ECR plasmas show reduced photoluminescence intensity. The extent of the degradation depends on both the microwave power level and any additional r.f. power applied to increase the energy of ions in the discharge. Annealing at 200°C restores approx. one-third of the initial luminescence efficiency in both materials, but HF removal of the native oxide increases the PL intensity to ∼80% in InGaAs and ∼40% in InP. The mechanism for the degraded optical output from these materials is creation of both interface and bulk states. The latter are present to depths of ≥200 A and are more prevalent in InP. Passivation of the surfaces using (NH 4 ) 2 S treatment completely restores the PL intensity in InGaAs, but not in InP. ECR deposition of SiN x shows excellent conformity around the gate contact of submicron high electron mobility transistors, and an absence of the rabbit-ears typically present with conventional PECVD.

Effect of ECR plasma on the luminescence efficiency of InGaAs and InP

Innovative silicon concepts and nonsilicon materials such as SiC, diamond and group-III nitrides are finding interest for new generations of electronic devices operational at much higher voltages and temperatures than conventional lower-power transistors and integrated circuits. Improved bulk and epitaxial growth, processing, device design and circuit architecture, bonding, testing and packaging are all necessary for realization of new applications. It seems clear from the symposium that Si will continue to dominate most power electronics applications for the next decade, while SiC is by far the most mature of the newer materials technologies. The group-III nitrides are also extremely attractive because of their excellent transport properties and the availability of heterostructures. It is likely that hybrid GaN/SiC devices will have a role due to the need for high thermal conductivity substrates for thermal management. Diamond appears to be trailing because of the inability to dope with donor impurities, although in principle, its properties are probably better suited to high-temperature applications than many other materials. Summaries of these topics are provided by invited review papers, while contributed and poster papers describe work in progress. Topics include: new boule growth techniques for ultra-high-purity Si and wide-bandgap materials; CVD and epitaxial techniques for powermore » materials; high-power/high-temperature device structures; advanced wafer-scale thermal management; simulation tools specific to high-power devices; advanced processing techniques; and packaging/testing at high currents/temperatures.« less

Fan Ren

Papers

The incorporation of hydrogen into III–V nitrides during processing

Method of making a GaAs-based laser comprising a facet coating with gas phase sulphur

Investigation of wet etching solutions for In0.5Ga0.5P

Effect of ECR plasma on the luminescence efficiency of InGaAs and InP

Power semiconductor materials and devices