Conductivity and hall-effect in highly resistive GaN layers

Highly resistive GaN layers grown by molecular beam epitaxy are characterized by temperature dependent conductivity and Hall effect measurements. Samples with rho(300) congruent to 3 x 10(3) Ohm cm show room temperature Hall mobility of 22 and 35 cm(2) V-1 s(-1) and have a temperature dependence mu(H) similar to T-x with x = 0.9 and 0.5. This is in contradiction to a sample with rho(300) congruent to 32 Ohm cm which has a room temperature mobility of 310 cm(2) V-1 s(-1) and a mu(H) similar to T-x with x = -1.4. The same activation energy of 0.23 eV, attributed to donor-like defects, is found for all three samples investigated. Temperature dependent conductivity data can be reasonably fitted considering band conduction. The presence of various hopping mechanisms is discussed. (C) 2000 American Institute of Physics. [S0003-6951(00)02825-4]

Bias-assisted photoelectrochemical etching of p-GaN at 300 K

Photoelectrochemical (PEC)etching of p-type GaN has been realized in room temperature, 0.1 M KOH solutions. PECetching of GaN was achieved by applying a positive bias to the surface of the p-GaN layer through a deposited titanium mask. The applied bias reduces the field at the semiconductor surface, which induced the dissolution of the GaN. The effect of bias on etch rate and morphology was examined. It was found that insulating the Ti mask from the KOH solution with Si3N4 significantly increases the etch rate. The rms roughness of the etched region decreased as the bias voltage increased. Etch rates as high as 4.4 nm/min were recorded for films etched at 2 V

Conductivity and hall-effect characterization of highly resistive molecular-beam epitaxial GaN layers

Highly resistive molecular beam epitaxial GaN layers are characterized by temperature dependent conductivity and Hall effect measurements. Seven n-type GaN samples with room temperature layer resistivity ranging between 8 and 4.2x10(6) Omega cm are used in this study. The experimental data are analyzed by considering various transport models such as band and hopping conduction, scattering on charged dislocations and grain boundaries controlled transport. The same defect level of 0.23 eV, attributed to nitrogen vacancy, is found for layers with rho (300)less than or equal to3.7x10(3) Omega cm. The Hall mobility for two lower resistivity layers is influenced mainly by phonon scattering (mu (H)similar toT(x), x=-1.4). However, higher resistivity layers show positive mobility power, x=0.5-0.9, which can be explained by dominating scattering on charged dislocations. Properties of layers with the highest resistivity (1x10(5) and 4.2x10(6) Omega cm) and extremely low Hall mobility (6 and <0.1 cm(2) V-1 s(-1)) are consistent with grain boundary controlled transport. The barrier height between grains of 0.11 eV and an average grain size of 200 nm are found. Neither nearest-neighbor or variable range single phonon hopping nor multiphonon hopping can be clearly attributed to the conduction of the layers investigated. (C) 2000 American Institute of Physics. [S0021-8979(00)03923-2]

Conductivity and hall-effect in highly resistive GaN layers

Highly resistive GaN layers grown by molecular beam epitaxy are characterized by temperature dependent conductivity and Hall effect measurements. Samples with rho(300) congruent to 3 x 10(3) Ohm cm show room temperature Hall mobility of 22 and 35 cm(2) V-1 s(-1) and have a temperature dependence mu(H) similar to T-x with x = 0.9 and 0.5. This is in contradiction to a sample with rho(300) congruent to 32 Ohm cm which has a room temperature mobility of 310 cm(2) V-1 s(-1) and a mu(H) similar to T-x with x = -1.4. The same activation energy of 0.23 eV, attributed to donor-like defects, is found for all three samples investigated. Temperature dependent conductivity data can be reasonably fitted considering band conduction. The presence of various hopping mechanisms is discussed. (C) 2000 American Institute of Physics. [S0003-6951(00)02825-4]

Very High Channel Conductivity in Low-Defect AlN/GaN High Electron Mobility Transistor Structures

Low defect AlN/GaN high electron mobility transistor (HEMT) structures, with very high values of electron mobility (\u3e1800 cm2/V s) and sheet charge density (\u3e3×1013 cm−2), were grown by rf plasma-assisted molecular beam epitaxy (MBE) on sapphire and SiC, resulting in sheet resistivity values down to ∼ 100 Ω/◻ at room temperature. Fabricated 1.2 μm gate devices showed excellent current-voltage characteristics, including a zero gate saturation current density of ∼ 1.3 A/mm and a peak transconductance of ∼ 260 mS/mm. Here, an all MBE growth of optimized AlN/GaN HEMT structures plus the results of thin-film characterizations and device measurements are presented

Risk factors of occupational accidents in units of storage and industrialization of rice

The aim of the study was to evaluate the risks of occupational accidents in units of processing and storage of rice in Rio Grande do Sul and to check compliance with safety standards. The rice processing industry accounts for more than 8000 direct jobs. The work generates wealth and knowledge, but, unfortunately, can also generate accidents and illnesses. The cost of an accident, besides causing loss of life, or inability to work, temporary or permanent, can bring large losses to the worker, his family and the state. In the present study are described in seven fatal accidents at work, increases in processing industries. These reports illustrate that protection of workers should not only rest on the lessons learned, but also should be made primarily in prevention. Of the 267 industries in activity in regions rice farms, covering 77 municipalities in Rio Grande do Sul, were assessed 36 (13.5%), through data collection, interviews and visits to the industrial park. It was noted the difficulty for the full deployment of security work, due to several factors such as need for investment, facilities, and personnel training, behavioral addictions and legal requirements. While the laws have more than 30 years, concern and commitment of the companies with the concept of job security needs to be increased.Objetivou-se, com o trabalho, avaliar os riscos de acidentes do trabalho em unidades de beneficiamento e armazenamento de arroz no Rio Grande do Sul e verificar a observância às normas de segurança. O setor de beneficiamento de arroz é responsável por mais de 8000 empregos diretos. O trabalho gera riquezas e conhecimento, mas, infelizmente, pode gerar também acidentes e doenças. O custo de um acidente, além de causar a perda de uma vida, ou a incapacidade laboral, temporária ou permanente, poderá trazer inúmeros prejuízos para o trabalhador, sua família e ao Estado. Na presente pesquisa são descritos sete acidentes fatais do trabalho, ocorridos em indústrias de beneficiamento. Estes relatos ilustram que a proteção dos trabalhadores não só deve repousar sobre as lições aprendidas, mas, também deve ser constituída, prioritariamente, em ações preventivas. Das 267 indústrias em atividade nas regiões arrozeiras, abrangendo 77 municípios no Estado do Rio Grande do Sul, foram avaliadas 36 (13,5%), através de levantamento de dados, entrevistas e visitas ao parque industrial. Constatou-se a dificuldade para a total implantação da segurança do trabalho, devido a diversos fatores tais como: necessidade de investimentos, equipamentos, instalações e treinamento de pessoal; vícios comportamentais e exigências legais. Apesar de as leis terem mais de 30 anos, a preocupação e o comprometimento das empresas com o conceito de segurança do trabalho necessitam ser aumentados

Surface passivation of AlN/GaN MOS-HEMTs using ultra-thin Al2O3 formed by thermal oxidation of evaporated aluminium

A simple method is reported for fabrication of AlN/GaN MOS-HEMTs. Ultra-thin Al2O3, which is formed using thermal oxidation of evaporated Al, was used for surface passivation and as a gate dielectric. Prior to formation of Al2O3, the Al protects the very sensitive AlN epilayer from exposure to processing liquid chemicals. Fabricated two-finger AlN/GaN MOS-HEMTs with 3 mm gate length and 200 mm gate width showed good gate control of drain currents up to a gate bias of 3 V and achieved a maximum drain current, I-DSmax, of similar to 900 mA/mm. The peak extrinsic transconductance, G(max), of the device is similar to 100 mS/mm at V-DS = 8 V. Capacitance-voltage (C-V) characteristics of Al2O3/AlN/GaN circular test MOS structures were observed and measured. They exhibited no hysteresis, indicating the good quality of the thermally grown Al2O3 for realising AlN/GaN MOS-HEMTs for high power and high frequency applications