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Student Number 87242003
Author Li-Shei Yeh(߾)
Author's Email Address No Public.
Statistics This thesis had been viewed 1987 times. Download 1486 times.
Department Physics
Year 2002
Semester 2
Degree Ph.D.
Type of Document Doctoral Dissertation
Language English
Title The dark current and the exciton effect of GaN p-i-n photodetectors
Date of Defense 2003-07-10
Page Count 85
Keyword
  • dark current
  • GaN
  • p-i-n
  • photodetectors
  • photodiode
  • Abstract For this dissertation, we investigated the mechanism of the dark current for GaN p-i-n (PIN) photodetectors. The exciton effect to responsivity was also studied. We compared theoretical calculations with the experimental data. We found the dark current to be dominated by the generation-recombination current and the trap-assisted tunneling current. The dark current is dominated by the generation-recombination mechanism below 8V reverse bias. An exponential increase in the dark current beyond 8V can be attributed to the trap-assisted tunneling current (indirect tunneling). The traps mainly come from the acceptor impurity level (0.145eV). Beyond 30V, the dark current may be attributed to trap donor levels of 0.43eV and 0.7eV below the conduction band.
    Two types of p-layers structures were also studied, one with a thick p-layer (700nm) and the other with a p-layer thickness of only 50nm. In the thick p-layer homojunction p-i-n photodiodes, we observed a peak for the responsivity-wavelength curve at 363nm. However, a flat responsivity curve was observed for the thin p-layer (50nm) homojunction p-i-n photodiodes. The thinner p-layer constricted the tip (exciton) absorption phenomenon of the depletion region current and the diffusion current on the n-side, because of the thin penetration depth of the GaN material and the short diffusion length of the p-type GaN. We determined the peak (exciton effect) of the responsivity from measurements and the calculations at room temperature. The GaAs material showed no such phenomenon because the exciton does not exist at RT.
    The properties of the superlattices (SLs) in p-layer samples and the In-doped in i-layer samples are investigated. The SLs p-layer could achieve the high hole concentration and low resistivity. The high hole concentration of the p-layer GaN p-i-n leads a slight depletion in the p-layer slightly when operate at reverse bias. The high breakdown voltage could be achieved using the thin p-layer, that reduced useless absorption (could not be transferred to the photocurrent). The high hole concentration increased the breakdown voltage and simultaneously reduced useless absorption. The shorter p-layer diffusion time was owed to the lower resistivity of the p-layer. However we designed large geometry devices which caused that the response time dominated by the RC delay time. We could not be sure that the diffusion time had improved. On the other hand, the In-doped i-layer included isoelectronic impurities which induced the dark current of one order of magnitude greater than the unintentionally doped sample for reverse bias. The isoelectronic impurity effect was more than the material quality improvement for reverse dark current. An absence of improvement in the dark current was observed. However we did observe an improvement in the material quality (low ideality factor 1.75 and series resistance 0.3k[) for forward bias.
    Our GaN homojunction p-i-n photodiode showed several good properties indicated as follows (1) a low dark current density of 0.3nA/cm2 at -7.5V, (2) a high responsivity of 0.1 A/W (353nm) at 0V, (3) a fast response time of 7.1 ns at 0V.
    Table of Content Content
    Abstract (in Taiwanese)KKKKKKKKKKKKKKK.K.KKK..I
    Abstract (in English)KKKKKKKKKKKKKKKK.KKKK..III
    AcknowledgementsKKKKKKKKKKKKKKKKK.KKKKV
    ContentKKKKKKKKKKKKK.KKKKKKKKKKKK..VI
    Table captionsKKKKKKKKKKKKKKKKKK..KKKK.VII
    Figure captionsKKKKKKKKKKKKKKKKKKKKKK.VIII
    1.IntroductionKKKKKKKKKKKKKKKKKKKKKKK.1
    1.1Introduction of GaN p-i-n photodetectorKKKKKKKKKK1
    1.2The aim of this dissertationKKKKKKKKKKKKKKK.2
    2.Experimental techniques and measurement setupKKKKKKKK...6
    2.1Device processesKKKKKKKKKKKKKKKKKKK.6
    2.2Measurement setupKKKKKKKKKKKKKKKKKK.8
    2.3Material characterizationKKKKKKKKKKKKKKKK9
    3.Characteristics of GaN p-i-n with a p-layer AlGaN/GaN superlattice..12
    3.1MotivationKKKKKKKKKKKKKKKKKK...KK..12
    3.2Dark current and photocurrent characteristicsKKKK..............13
    3.3Responsivity characteristicsKKKKKKKK.KKKKKK15
    3.4Response time measurementKKKKKKKKKK.KKK...16
    3.5Capacitance-voltage measurementKKKKKKK.KKKK..19
    3.6SummaryKKKKKKKKKKKKKKKKKK.KKK.19
    4.Characteristics of GaN p-i-n with In-doping in i-layerKK.KKK.22
    4.1IntroductionKKKKKKKKKKKKKKKK.KKKK.22
    4.2Current-voltage characteristicsKKKKKKKKK.KKKK23
    4.3Characteristics of spectral photoresponseKKK.KKKKK...25
    4.4Capacitance-voltage measurementKKKKKK.KKKKK..25
    4.5Response timeKKKKKKKKKKKKKKKKKKK..25
    4.6SummaryKKKKKKKKKKKKKKKK.KKKKK.26
    5.Dark current and exciton effect of GaN p-i-n photodetectorKK.K.28
    5.1IntroductionKKKKKKKKKKKKKKKKKK.KK.28
    5.2Calculation and characteristics of dark currentKKKKK.K...29
    5.3Exciton effect of responsivityKKKKKKKK.......................33
    5.4SummaryKKKKKKKKKKKKKKKKKK.KKK.37
    6.Conclusion............................................................................KKK...40
    Bibliography.............................................................................................43
    Publication ListKKK..KKKKKKKKKKKKK..KK.KKK84
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    1.G. Yu, G. Wang, T. Soga and T. Egawa, Appl. Phys. Lett. 70, 3209(1997).
    2.J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey and B.P. Keller, Appl. Phys. Lett. 71, 2572(1997).
    3.M. J. Bergmann, J. F. Muth, R. A. Rao and M. Schurman, Appl. Phys. Lett. 74, 3188(1999).
    4.G. Y. Xu, A. Salvador, G. Smith and B. Goldenberg, Appl. Phys. Lett. 71, 2154(1997).
    5.A. Osinsky, S. Gangopadhyay, R. Gaska and D. Kuksenkov, Appl. Phys. Lett. 71, 2334(1997).
    Advisor
  • Gou-Chung Chi()
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    Date of Submission 2003-07-16

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