Observation of Midgap States in GaN with Optical-Isothermal Capacitance Transient Spectroscopy

ABSTRACTOptical-isothermal capacitance transient spectroscopy (O-ICTS) was used to distinguish the deep levels which occur in unintentionally doped n-type GaN by means of their characteristic optical cross section. GaN grown by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) were compared. Correspondence between optical and thermal emission characteristics of previously discovered levels, E2 (∼Ec-0.55 eV) and E4 (∼EC-1.0 eV), were clearly determined by observing their sequential appearance in the ICTS spectra. Whether by thermal or optical stimulation, the emission from E4 was found to be broad in nature; it is consequently believed to involve a defect. The total measured concentration of deep levels, including a prominent level which photoionizes in the range 2.5 to 3.0 eV below the conduction band, is greater in the GaN grown by MOVPE than by HVPE that was tested.

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Deep levels in n-type AlGaN grown by hydride vapor-phase epitaxy on sapphire characterized by deep-level transient spectroscopy

Applied Physics Letters ◽

10.1063/1.2137901 ◽

2005 ◽

Vol 87 (22) ◽

pp. 222112 ◽

Cited By ~ 33

Author(s):

J. Osaka ◽

Y. Ohno ◽

S. Kishimoto ◽

K. Maezawa ◽

T. Mizutani

Keyword(s):

Vapor Phase ◽

Deep Level Transient Spectroscopy ◽

Deep Level ◽

Vapor Phase Epitaxy ◽

Deep Levels ◽

Hydride Vapor Phase Epitaxy ◽

Transient Spectroscopy

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Transient Capacitance Characterization of Deep Levels in Undoped and Si-Doped GaN

MRS Proceedings ◽

10.1557/proc-764-c3.39 ◽

2003 ◽

Vol 764 ◽

Author(s):

S. Nakamura ◽

P. Liu ◽

M. Suhara ◽

T. Okumura

Keyword(s):

Chemical Vapor ◽

Deep Levels ◽

Yellow Luminescence ◽

Capacitance Measurements ◽

Transient Capacitance ◽

Si Doped ◽

Transient Spectroscopy ◽

Capacitance Transient ◽

Isothermal Capacitance Transient Spectroscopy

AbstractThe deep levels in both undoped and Si-doped GaN layer grown by metalorganic chemical vapor deposition have been characterized by photocapacitance and transient capacitance spectroscopy. The increase in the photocapacitance was observed in both GaN samples in the range of 1.8 to 2.2 eV. This is due to the photoionization of carriers from the deep levels associated with the yellow luminescence (YL). In addition, the transient capacitance measurements after the photoionization were also performed in the range of 1.8 to 3.4 eV. The notable transient of capacitance was observed at the photon energies of about 2.1 and 3.4 eV, the former could be associated with the change in the charge state of the YL center and latter might stem from some other defects capturing photogenerated carriers. By using the isothermal capacitance transient spectroscopy (ICTS) analysis, the ICTS peaks due to the deep levels associated with YL were detected at about t = 150 s in both GaN samples. In addition, another ICTS peak was detected only in the Si-doped GaN samples. It is considered that this peak is associated with the deep levels deeper than YL levels and the deeper levels originate from defects induced by Si doping.

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