Publications by    
Page 1  (11 Items)

1.  AlxGa1-xN Materials and Device Technology for Solar Blind Ultraviolet Photodetector Applications
R. McClintock, P. Sandvik, K. Mi, F. Shahedipour, A. Yasan, C. Jelen, P. Kung, and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 4288, pp. 219-- January 22, 2001
There has been a growing interest for the development of solar blind ultraviolet (UV) photodetectors for use in a variety of applications, including early missile threat warning, flame monitoring, UV radiation monitoring and chemical/biological reagent detection. The AlxGa1-xN material system has emerged as the most promising approach for such devices. However, the control of the material quality and the device technology are still rather immature. We report here the metalorganic chemical vapor deposition, the n-type and the p-type doping of high quality AlxGa1-xN thin films on sapphire substrates over a wide range of Al concentration. reprint
 
2.  AlxGa1-xN for Solar-Blind UV Detectors
P. Sandvik, K. Mi, F. Shahedipour, R. McClintock, A. Yasan, P. Kung, and M. Razeghi
Journal of Crystal Growth 231 (2001)-- January 1, 2001
We report on the metalorganic chemical vapor deposition of high quality AlGaN thin films on sapphire substrates over a wide range of Al concentrations. The quality of these AlGaN materials was verified through a demonstration of high performance visible and solar-blind UV p–i–n photodiodes with peak cutoff wavelengths ranging from 227 to 364 nm. External quantum efficiencies for these devices reached as high as 69% with over five orders rejection ratio from the peak to visible wavelengths. reprint
 
3.  Lateral Epitaxial Overgrowth of GaN on Sapphire and Silicon Substrates for Ultraviolet Photodetector Applications
M. Razeghi, P. Sandvik, P. Kung, D. Walker, K. Mi, X. Zhang, V. Kumar, J. Diaz, and F. Shahedipour
-- May 1, 2000
 
4.  Solar-Blind AlxGa1-xN p-i-n Photodetectors grown on LEO and non-LEO GaN
P. Sandvik, D. Walker, P. Kung, K. Mi, F. Shahedipour, V. Kumar, X. Zhang, J. Diaz, C. Jelen, and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 3948, pp. 265 -- January 26, 2000
The III-Nitride material system is an excellent candidate for UV photodetector applications due to its wide, direct bandgaps and robust material nature. However, despite many inherent material advantages, the III-Nitride material system typically suffers from a large number of extended defects which degrade material quality and device performance. One technique aimed at reducing defect densities in these materials is lateral epitaxial overgrowth (LEO). In this work, we present a preliminary comparison between AlGaN UV, solar-blind p-i-n photodiodes fabricated form LEO GaN and non-LEO GaN. Improvements in both responsivity and rejection ratio are observed, however, further device improvements are necessary. For these, we focus on the optimization of the p- i-n structure and a reduction in contact resistivity to p- GaN and p-AlGaN layers. By improving the structure of the device, GaN p-i-n photodiodes were fabricated and demonstrate 86 percent internal quantum efficiency at 362 nm and a peak to visible rejection ratio of 105. Contact treatments have reduced the contact resistivity to p-GaN and p-AlGaN by over one order of magnitude form our previous results. reprint
 
5.  LEO of III-Nitride on Al2O3 and Si Substrates
M. Razeghi, P. Kung, P. Sandvik, K. Mi, X. Zhang, V.P. Dravid, J. Freitas, and A. Saxler
SPIE Conference, San Jose, CA, -- January 26, 2000
Lateral epitaxial overgrowth (LEO) has recently become the method of choice to reduce the density of dislocations in heteroepitaxial GaN thin films, and is thus expected to lead to enhanced performance devices. We present here the LEO growth and characterization of GaN films by low pressure metalorganic chemical vapor deposition. Various substrates were used, including basal plane sapphire and oriented Si substrates. The steps in the LEO growth technology will be briefly reviewed. The characterization results will be discussed in detail. The structural, electrical and optical properties of the films were assessed through scanning, atomic and transmission electron microscopy, x-ray diffraction, capacitance-voltage, deep level transient spectroscopy, photoluminescence, and scanning cathodoluminenscence measurements. Single-step and double- step LEO GaN was achieved on sapphire. Similarly high quality LEO grown GaN films were obtained on sapphire and silicon substrates. Clear and dramatic reduction in the density of defects are observed in LEO grown materials using the various characterization techniques mentioned previously. reprint
 
6.  Solar-blind AlGaN photodiodes with very low cutoff wavelength
D. Walker, V. Kumar, K. Mi, P. Sandvik, P. Kung, X.H. Zhang, and M. Razeghi
Applied Physics Letters 76 (4)-- January 24, 2000
We report the fabrication and characterization of AlxGa1–xN photodiodes (x~0.70) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The peak responsivity for –5 V bias is 0.11 A/W at 232 nm, corresponding to an internal quantum efficiency greater than 90%. The device response drops four orders of magnitude by 275 nm and remains at low response for the entire near-ultraviolet and visible spectrum. Improvements were made to the device design including a semitransparent Ni/Au contact layer and a GaN:Mg cap layer, which dramatically increased device response by enhancing the carrier collection efficiency. reprint
 
7.  Future Trends of III-Nitrides Using Lateral Epitaxial Overgrowth
M. Razeghi, P. Kung, P. Sandvik, X. Zhang, K. Mi, D. Walker, V. Kumar, and J. Diaz
-- December 14, 1999
 
8.  Development of High-performance III-Nitride-based Semiconductor Devices
M. Razeghi, P. Kung, D. Walker, E. Monroy, M. Hamilton, and P. Sandvik
-- June 1, 1999
 
9.  AlxGa1-xN p-i-n Photodiodes on Sapphire Substrates
D. Walker, P. Kung, P. Sandvik, J. Wu, M. Hamilton, I.H. Lee, J. Diaz, and M. Razeghi
SPIE Conference, San Jose, CA, -- January 27, 1999
We report the fabrication and characterization of AlxGa1-xN p-i-n photodiodes (0.05 ≤ to X ≤ 0.30) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The devices present a visible-rejection of about four orders of magnitude with a cutoff wavelength that shifts from 350 nm to 291 nm. They also exhibit a constant responsivity for five decades (30 mW/m² to 1 kW/m²) of optical power density. Using capacitance measurements, the values for the acceptor concentration in the p-AlxGa1-xN region and the unintentional donor concentration in the intrinsic region are found. Photocurrent decays are exponential for high load resistances, with a time constant that corresponds to the RC product of the system. For low load resistances the transient response becomes non-exponential, with a decay time longer than the RC constant. reprint
 
10.  Schottky MSM Photodetectors on GaN Films Grown on Sapphire by Lateral Epitaxial Overgrowth
P. Kung, D. Walker, P. Sandvik, M. Hamilton, J. Diaz, I.H. Lee and M. Razeghi
SPIE Conference, San Jose, CA, -- January 27, 1999
We report the growth and characterization of Schottky based metal-semiconductor-metal ultraviolet photodetectors fabricated on lateral epitaxially overgrown GaN films. The lateral epitaxial overgrowth of GaN was carried out on basal plane sapphire substrates by low pressure metalorganic chemical vapor deposition and exhibited lateral growth rates more than 5 times as high as vertical growth rates. The spectral responsivity, the dependence on bias voltage, on incident optical power, and the time response of these photodetectors have been characterized. Two detector orientations were investigated: one with the interdigitated finger pattern parallel and the other perpendicular to the underlying SiOx mask stripes. reprint
 
11.  Development of High-performance III-Nitride-based Semiconductor Devices
M. Razeghi, P. Kung, D. Walker, M. Hamilton, and P. Sandvik
-- November 6, 1998
 

Page 1  (11 Items)