Author: Chung-Han Lin
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ISBN:
Category :
Languages : en
Pages :
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Our DRCLS, SPS, time-resolved SPS (t-SPS), current-voltage-temperature (I-V-T) shows that fast and thermal neutron preferentially affect device properties. Fast neutron will induce defects in GaN by recoil and displacement damage whereas thermal neutron tends to enhance the interaction between metal/semiconductor interfaces due to heat. Time-resolved surface photovoltage spectroscopy (t-SPS) results reveal a defect evolution of GaN under fast neutron irradiation that indicates low fast neutron dosage will enhance GaN properties a result which is confirmed by DRCLS results. XPS results show that Ti and Ni are more resistant than other metal but will interact with GaN at higher thermal neutron fluence. Our results show that fast and thermal neutrons are both detrimental electronic devices without proper protection.
Author: Dennis Eugene Walker
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ISBN:
Category : Cathodoluminescence
Languages : en
Pages : 217
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Abstract: The AlGaN/GaN material system is ideally suited for UV detectors, light sources, and high performance, high power transistors. Through an understanding of the physics and device properties associated with defects, engineered solutions can allow the utilization of the full potential of AlGaN/GaN device properties. Auger Electron Spectroscopy (AES) and secondary electron threshold (SET) techniques allow the characterization of band bending and work function at semiconductor surfaces. Using these techniques with ultra-high vacuum (UHV) sample cleaving and metal deposition, Schottky barrier formation to non-polar GaN was investigated revealing cases of both ideal band-bending and Fermi level pinning. Cathodoluminescence spectroscopy (CL) allows the investigation of luminescent defect levels with depth-resolving capability by controlling the incident beam voltage and associated electron beam penetration into the sample. High electron mobility transistors (HEMTs) exhibiting current collapse were investigated using CL and CL mapping and specific defects were found in the GaN channel and buffer regions that may help explain the current collapse phenomena. Coupling a novel gate mask into a typical HEMT fabrication sequence and utilizing three, independent UHV sample cleaning techniques including thermal desorption of contaminants, Ga-reflux, and N2 ion sputtering, and metallization of the gates on AlGaN/GaN HEMTs, correlations in defect levels, surface cleaning technique, and finished device performance were found. In analyzing the CL data for this sample, however, a specific feature located just below the GaN near band edge was observed to accumulate near the Ohmic contacts prompting a further investigation of both the effects of the RIE etch used in producing the UHV-compatible mask as well as four different Ohmic contact structures on both defect levels determined by CL and on final device performance. Finally, a bulk GaN sample was processed with Ohmic contacts to determine the correlation of the AlGaN device layer in the formation of this defect level associated with the Ohmic contacts and the role of the mesa RIE etch on the same defect. Through these investigations, progress in the underlying physics of Schottky barrier formation on GaN and the important role of defects on device performance using AES, SET, and CL have been demonstrated.
Author: Monta Raymond Holzworth (Jr)
Publisher:
ISBN:
Category :
Languages : en
Pages : 192
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Book Description
AlGaN/GaN high electron mobility transistors are unique for their combination of high temperature, high power, and high frequency applications. Compared to Si, Ge, and compound semiconductors such as GaAS and InP, AlGaN/GaN transistors outclass the current technology due to their superior combination of high breakdown voltage and high frequency performance. These characteristics arise from structural and electrical properties inherent to the AlGaN/GaN heterojunction which have enabled AlGaN/GaN transistors usage in important military and civilian applications such as microwave and millimeter technology, RADAR systems, and as high current and voltage switches in utility grid systems. As the technology continues to improve due to increased materials quality and device advancements, future applications will require AlGaN/GaN transistor usage under even higher voltages and temperatures. Therefore, the effects of these stresses need to be investigated in order improve device performance and reliability.
Author: Troy A. Uhlman
Publisher:
ISBN:
Category : Field-effect transistors
Languages : en
Pages : 340
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Author: Tania Roy
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 101
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Author:
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ISBN:
Category : Chemistry
Languages : en
Pages : 2002
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Author: Anupama Yadav
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ISBN:
Category :
Languages : en
Pages : 107
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In this study, the fundamental properties of AlGaN/GaN based High Electron Mobility Transistors (HEMTs) have been investigated in order to optimize their performance in radiation harsh environment. AlGaN/GaN HEMTs were irradiated with 60Co gamma-rays to doses up to 1000 Gy, and the effects of irradiation on the devices' transport and optical properties was analyzed. Understanding the radiation affects in HEMTs devices, on carrier transport, recombination rates and traps creation play a significant role in development and design of radiation resistant semiconductor components for different applications.
Author:
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ISBN:
Category :
Languages : en
Pages : 15
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Author: Sameer Jayanta Joglekar
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ISBN:
Category :
Languages : en
Pages : 161
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Book Description
Gallium Nitride (GaN) belongs to a class of materials called wide band-gap semiconductors. In recent years, the versatile nature of this material has been exploited for a wide range of applications from solid state lighting to RF and microwave communication, as well as high power switching. The first part of this thesis discusses planar AlGaN/GaN transistors. GaN is a piezoelectric material, and changes in mechanical stress result in a change in the charge density which in turn affects the maximum current in AlGaN/GaN transistors. Finite element modelling techniques were applied to quantify the mechanical stress distribution in planar AlGaN/GaN RF transistors resulting from device fabrication, and operation in the on- and off-state. Thereafter, two important surface and interface effects were studied in this thesis. In the first one, the impact of surface cleanings, surface treatments and plasma-based dry etch conditions on two different types of ohmic contact technologies was investigated. Contact resistance measurements were correlated with surface characterization results. The second was that of interface positive charges at the Al2O3-GaN interface and the increase in electron density in the device resulting from them. In both these problems, a combination of device electrical measurements and material characterization techniques was used to establish direct correlations between device behavior and material properties. The second part of the thesis deals exclusively with nano-ribbon (NR) or fin-like AlGaN/GaN transistors. Fundamental transport properties of charge density and mobility in NR devices were studied in order to understand the difference in behavior of these devices from planar devices. The influence of passivation films on the charge density in these structures was investigated, using Al2O3 passivation as a specific example. Electron mobility degradation due to sidewall-scattering in NR devices was quantified using different mobility extraction methods based on device measurements. The thesis concludes with a potential application of NR AlGaN/GaN transistors for high linearity power amplification. A new kind of transistor with varying threshold voltages along the gate width is proposed to improve the DC and RF linearity of GaN-based devices.
Author:
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ISBN:
Category :
Languages : en
Pages : 4
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Current collapse is observed to be induced in AlGaN/GaN high-electron-mobility transistors as a result of short-term bias stress. This effect was seen in devices grown by both metalorganic chemical vapor deposition (MOCVD) and molecular-beam epitaxy (MBE). The induced collapse appears to be permanent and can be reversed by SiN passivation. The traps responsible for the collapse have been studied by photoionization spectroscopy. For the MOCVD-grown devices, the same traps cause the collapse in both unstressed and stressed devices. These effects are thought to result from hot-carrier damage during stress.
