The temperature-dependent Hall measurement was performed on the undoped GaN thin films grown by molecular beam epitaxy. The mobility and electron density were obtained by the T-dependent ( 4.2K~300K ) Hall measurement at magnetic field 300mT. Since the Hall coefficient is the ratio of the perpendicular electric field to the product of current density and magnetic field, we calculate the mobility and electron density to get the temperature-dependent mobility and electron density curves. We change the N/Ga ratio on the epilayer of two samples and analysis the mobility and carrier density against temperature. The sample growth procedure were (1)nitridation for 60 min, with ,at .(2) low temperature GaN buffer layer growth for 2 min, with ,at , and (3)high temperature GaN epilayer growth for 3hr, at . The N/Ga ratio of the samples are 30 and 35.

<p>Gallium Nitride based devices due to their inherent material properties are considered as one of the most promising devices to realize high power, high frequency transistors with lower power consumption in next-generation applications. Although the technology has been studied since early 1970s, there is still a vast room and expectations in its yet unachieved findings. In present work the GaN technology is explored and state-of-the-art studies of GaN based HEMTs and their application in MMICs are presented. Different designs are presented and evaluated and the results are reported. In particular the HEMT performance is studied in terms of DC in addition to large signal conditions, where the device’s performance becomes function of power levels it is driven with. The peculiarities and challenges of building an automated Load-Pull setup are outlined and analysis for further improvements is presented.</p>

Gallium Nitride based devices due to their inherent material properties are considered as one of the most promising devices to realize high power, high frequency transistors with lower power consumption in next-generation applications. Although the technology has been studied since early 1970s, there is still a vast room and expectations in its yet unachieved findings. In present work the GaN technology is explored and state-of-the-art studies of GaN based HEMTs and their application in MMICs are presented. Different designs are presented and evaluated and the results are reported. In particular the HEMT performance is studied in terms of DC in addition to large signal conditions, where the device’s performance becomes function of power levels it is driven with. The peculiarities and challenges of building an automated Load-Pull setup are outlined and analysis for further improvements is presented.

In this paper we will discuss the characteristic of AlGaN/GaN heterostructure grown on sapphire by plasma-assisted molecular-beam epitaxy. In this series of samples, we try to change the ratio of buffer layer N/Al, the ratio from sample A to sample D is 43¡B26¡B23¡B12. We used the Hall measurement¡BAFM and X-ray to analyze the series of samples. From the Hall measurement and AFM, we found that the dislocation scattering is the mainly reason which cause the mobility increasing or decreasing. From X-ray, we can get that the mainly dislocation type is edge dislocation. The density of edge dislocation decreased due to vary the growth conditions. In our samples, the mobility in the room temperature increase from 387 cm2/Vs to 1224 cm2/Vs and in the liquid nitrogen temperature the mobility achieve 3705 cm2/Vs.

In this thesis we reveal that the Ohmic contacts of n-type and p-type GaN are obtained by the method of thermal evaporation. For different types of GaN, different metals are used to evaporate on GaN surface to form Ohmic contact. The measurements of specific contact resistivity were performed by TLM (transmission line model) for different types of GaN. Also, we use a shadow mask to form four Ohmic contacts on four corners of GaN surface , and utilize the four contacts to perform Hall measurement by Van der Pauw method. By the data of Hall measurement, it indicates that the specific contact resistivity of heavily doped samples are smaller than lightly doped samples. The effect of intensity photoluminescence ( PL ) spectrum of different annealing treatment of p-type GaN are also demonstrated in this thesis. And the carrier concentration of p-type GaN will change with different annealing condition. The method of C-V analysis is a powerful technique to determine the parameters of device. In this thesis, we exhibit completed formulation of how to calculate all the parameters of MOS structure, using Ga2O3/p-GaAs MOS structure as calculated sample. The high frequency C-V curve of Ta2O5/n-GaN MOS structure reveals a possibility for fabricating a MOSFET using Ta2O5 as insulated layer and GaN as substrate. In this thesis, we utilize Ta2O5 as insulated material, because Ta2O5 is a material with high dielectric constan.

In this thesis, we grew undoped GaN and Si-doped GaN films on sapphire by metal organic chemical vapor deposition (MOCVD) system. For the purpose to investigate the influences of undoped GaN films, we modulated H2 gas flow rate and nitridation time in the undoped GaN growth conditions. The ramping rate, Si2H6 flow rate and undoped GaN film thickness were varied to study the influences on Si-doped GaN films. When H2 gas flow rate was increased, it led to carbon pollution reduced and improved films quality. Too long or too short nitridation time would change film qulity seriously. In the Si-doped GaN films growth, the films quality become worse when the ramping rate was too quick or too slow. The relationship between the carrier concentration of Si-doped GaN films and Si2H6 flow rate was linear. The electron mobility of Si-doped films will not increase apparently until Si2H6 flow rate up to 7.19nmol/min . Undoped GaN film which was pregrown before Si-doped GaN could improve the crystal quality of Si-doped GaN films, and it will influence the optical properties of Si-doped GaN film, such as PL spectra.

20 periods AlN/GaN distributed Bragg reflector (DBR) nanorod structure has been grown on Si (111) substrates at 780¢J by plasma-assisted molecular beam epitaxy (PAMBE) under highly N-rich conditions. The AlN/GaN DRB nanorod structure started with 637 nm high GaN nanorod directly grown on Si (111). Diameter of nanorod is around 80 nm. The height of nanorod is around 3.3 £gm, the density of nanorods is around 2¡Ñ1010 cm-2, and the thickness of each layer are around 44 nm and 58 nm for AlN and GaN, respectively. The nanorod had been analyzed by temperature dependent cathodoluminescence (CL), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), X-ray diffraction (XRD) measurement.

Thesis (M.A.)--University of Hong Kong, 2001.

As newer and more powerful technologies emerge in the market, the desire for compactness and aesthetics drive designers to aggressive new heights. The trend of technology is quite simply to deliver high-speed designs that pack more power while seeing reduction in form factor for ease of use at the consumer level. This presents new challenges with reliability, cost, and ultimately what the consumer strives for: performance. It is inevitable for a small compact size device, such as a smartphone or wireless repeater, to face heating issues when packing large amounts of power. The goal of this thesis is to characterize an in-market device’s thermal behavior and RF performance, and present an alternative design approach that helps improve thermal performance. This solution must not increase the design space or form factor excessively. The proposal utilizes an off-the-shelf solution and predicts performance improvements and degradation as a function of thermal performance. Electro-thermal simulators are used extensively to gauge the behavior and flow of heat within a gallium nitride device, and used as a baseline for comparison. Two modified approaches are presented and declared to be more efficient and reliable than the baseline. The design approaches comply with the industry standards of minimizing size and show a clear improvement in thermal behavior that can be utilized for any single device approach. The research is focused under similar power and biasing conditions so that designers can effectively implement a simple plug and play approach whenever the device under test is at risk of violating temperature limits and/or if performance degradation is observed under a variety of operating conditions.

Le nitrure de gallium (GaN) est un semi-conducteur à grand gap dont les propriétés en font un bon candidat pour remplacer le Si dans le domaine de l’électronique de puissance. Dans cette optique, cette thèse s’est intéressée à l’une des étapes de la conception d’une diode de puissance Schottky à base de GaN épitaxié sur Si : la gravure. L’objectif était alors de développer des procédés permettant une reprise de contact sur une couche enterrée de GaN n+. Ils devaient combiner des performances de gravure compatibles avec des processus industriels et conduire à des profils et états de surface adaptés à la réalisation d’un contact ohmique. La réalisation d’une structure pseudo-verticale, au travers de la gravure par la face supérieure d’une couche de 5 à 6 μm de GaN a été étudiée avec quatre réacteurs plasma différents. Des analyses du plasma et du matériau après gravure ont mis en évidence que le meilleur compromis était obtenu pour des plasmas inductifs en chimie chlorée avec une tension d’auto-polarisation modérée. Il a également été déterminé que l’ajout d’un gaz fluoré dans un plasma de ce type permettait de générer une passivation à même de protéger la surface du GaN. Pour répondre à la chute de vitesse de gravure qu’elle entraîne, un procédé alternant des étapes de gravure et de passivation a été développé et étudié. D’autre part, des recherches ont été menées afin de créer une structure verticale. Afin d’atteindre le GaN n+, des gravures en face arrière de vias de Si d’une profondeur de 300 μm par les procédés cryogéniques standard et STiGer anisotrope ont été effectuées. Un procédé de révélation permettant l’étude des couches composant le tampon, situé entre le Si et le GaN, a été mis au point. Leur gravure par des plasmas chlorés s’est révélée efficace au travers ou non de vias de Si. / Gallium nitride (GaN) is a wide bandgap III-V semiconductor with interesting electrical properties in order to replace Si in the field of power devices. The subject of this thesis was then to study one of the essential steps to realize a GaN based Schottky diode : the etch. The aim was to develop etching processes allowing the realization of an ohmic contact on an embedded GaN n+ layer. They must combine GaN etching performances compatible with industrial requirements and etch profiles and surface states compatible with an ohmic contact. The etching of a 5 to 6 μm GaN layer by four different reactors was studied in order to realize a pseudovertical structure. Plasma and GaN surfaces analyses were performed during and after etching by five developed and optimized processes. These analyses showed that best compromise was obtained for inductive chlorine plasmas with a moderate bias. The creation of a passivation layer which is able to protect GaN surface, thanks to fluorine addition in plasma chemistries was also established. To overcome the etch rate decreases induced by fluorine addition, a time multiplexed etching process, alternating etch and passivation steps, was developed and studied. Researches were also performed to achieve a vertical diode. Etching of 300 μm depth Si vias by standard cryogenic and anisotropic STiGer processes were carried out. A revelation process was also developed in order to study buffer layers etching. Effective buffer etching by chlorine plasma was demonstrated with or without Si vias.