Determination of AlGaN/GaN HEMT Reliability Using Optical Pumping as a Characterization Method
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Determination of AlGaN/GaN HEMT Reliability Using Optical Pumping as a Characterization Method D. Cheney1, R. Deist2, B. Gila2, F. Ren3, P. Whiting2, J. Navales1, E. Douglas2, and S. Pearton2 1
Electrical & Computer Engineering, University of Florida, 100 Center Drive, Gainesville, FL 32611, 352-219-0290, 352-846-2877 FAX, [email protected] 2 Material Science & Engineering, University of Florida, Gainesville, FL 32611 3 Chemical Engineering, University of Florida, Gainesville, FL 32611
ABSTRACT By pumping AlGaN/GaN HEMTs with below band-gap light we observe changes in drain current that correspond to the trapping and detrapping of carriers within the band-gap. These changes in drain current are indicators of trap density, since the energy from a specific wavelength of light pumps traps whose activation energies are less than or equal to that of the light source. AlGaN/GaN HEMTs on SiC with dual submicron gates with widths of 125nm, 140nm, or 170nm, are DC-stressed under three different conditions along a load line: VGS=0, VDS=5 (onstate), VGS=-2, VDS=9.2 and, VGS=-6, VDS=25 (off-state). The stress tests are interrupted at 20% degradation and the optically pumped comparisons to the baseline are measured. This paper describes the optical pumping technique and results from experiments of AlGaN/GaN HEMTs under the three DC stress biases along a load line. INTRODUCTION One of the main attractions to GaN semiconductors is its thermal stability due to its wide band-gap. Another benefit of wide band-gap III-V nitride devices is the ability to pump light from the visible spectrum with below-band-gap energy levels. Using visible light is attractive because of the availability of low cost light sources, such as lasers, at many different wavelengths. By pumping AlGaN/GaN HEMTs with below band-gap light we observe changes in drain current that correspond to the trapping and detrapping of carriers within the band-gap. Defect 1
3.41 eV
basal plane stacking faults on polar GaN [1] basal plane stacking faults on non-polar GaN [2] a-type threading dislocations [3]
Defect 2
3.34 eV
a-plane stacking faults [1]
Defect 3
3.28 eV
partial dislocations [1]
Defect 4
3.20 eV
CN [4]
Defect 5
2.9 eV
Blue defect - ON, dopants [5]
Defect 6
2.5 eV
Green defect - VGaON , dopants [5]
Defect 7
2.2 eV
Yellow defect - several vacancy defect models, VGa bound to dislocation, dopants [5]
Defect 8
2.21 eV
edge dislocations (screw dislocations are invisible) [6]
Defect 9
1.8 eV
Red defect - VNCN, implant damage, dopants [5]
Fig. 1. Band gap diagram of GaN with various traps
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These changes in drain current are indicators of trap density, since the energy from a specific wavelength of light pumps traps whose activation energies are less than or equal to that of the light source. Throughout the literature, several different types of line and point defects have been observed with a range of mid-gap energies [1-7]. Fig 1 illustrates defects from the visible range to the conduction band edge and is not considered a complete list
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