Photo-ionization spectroscopy of traps in AlGaN/GaN high-electron mobility transistors

Wolter, M.; Javorka, P.; Fox, A.; Marso, Michel; Lüth, H.; Kordoš, P.; Carius, R.; Alam, A.; Heuken, M.

doi:10.1007/s11664-002-0115-6

Cited by 10 publications

(13 citation statements)

References 12 publications

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“…Wolter et al [51] have also reported an interesting investigation of the effect on the photoionization spectra of gate bias and of the spatial separation between the 2DEG and the surface [50]. They observe that: (i) for devices where the 2DEG is closer to the AlGaN surface, the drain current is lower and the response function S(hν) in the photoionization spectrum is raised, suggesting a higher trap concentration, and (ii) as the gate bias is reduced (i.e.…”

Section: Photoionization Measurementsmentioning

confidence: 99%

Photoionization spectroscopy of deep defects responsible for current collapse in nitride-based field effect transistors

Klein

Binari

2003

J. Phys.: Condens. Matter

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This review is concerned with the characterization and identification of the deep centres that cause current collapse in nitride-based field effect transistors. Photoionization spectroscopy is an optical technique that has been developed to probe the characteristics of these defects. Measured spectral dependences provide information on trap depth, lattice coupling and on the location of the defects in the device structure. The spectrum of an individual trap may also be regarded as a 'fingerprint' of the defect, allowing the trap to be followed in response to the variation of external parameters. The basis for these measurements is derived through a modelling procedure that accounts quantitatively for the light-induced drain current increase in the collapsed device. Applying the model to fit the measured variation of drain current increase with light illumination provides an estimate of the concentrations and photoionization cross-sections of the deep defects. The results of photoionization studies of GaN metal-semiconductor field effect transistors and AlGaN/GaN high electron mobility transistors (HEMTs) grown by metal-organic chemical vapour deposition (MOCVD) are presented and the conclusions regarding the nature of the deep traps responsible are discussed. Finally, recent photoionization studies of current collapse induced by short-term (several hours) bias stress in AlGaN/GaN HEMTs are described and analysed for devices grown by both MOCVD and molecular beam epitaxy. Contents

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Section: Photoionization Measurementsmentioning

confidence: 99%

Photoionization spectroscopy of deep defects responsible for current collapse in nitride-based field effect transistors

Klein

Binari

2003

J. Phys.: Condens. Matter

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“…Power amplifiers based on AlGaN / GaN heterojunction field effect transistors ͑HFETs͒ are hampered by defects attributed to the AlGaN surface [1][2][3] and the GaN buffer [4][5][6] that exert detrimental influence upon device performance. Thus, quantitative observation of band gap states in AlGaN / GaN heterostructures provides an important metric for optimizing material growth and minimizing the impact of defects.…”

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confidence: 99%

“…Previous investigations pragmatically used HFETs themselves as a vehicle to study deep levels in AlGaN / GaN heterostructures, primarily focusing on the influence that pulsing of the gate-source bias or drain-source bias has on deep level activity and consequent degradation of pulsed versus dc I-V characteristics due to diminished two-dimensional electron gas ͑2DEG͒ sheet charge n s . Beyond those deep levels made apparent with bias modulation, additional band gap states can exist that affect n s and thereby device performance equally for both steady-state, pulsed, and rf operation and thus might not be observed using pulsing-based spectroscopy techniques such as drain current deep level transient spectroscopy 2,3 ͑I-DLTS͒ or photoionization induced current transient spectroscopy [4][5][6] ͑PICTS͒. Moreover, current-based techniques offer limited direct information regarding the location of defects within the heterostructure.…”

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confidence: 99%

Quantitative observation and discrimination of AlGaN- and GaN-related deep levels in AlGaN∕GaN heterostructures using capacitance deep level optical spectroscopy

Armstrong

Chakraborty

Speck

et al. 2006

Applied Physics Letters

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Deep levels were observed using capacitance deep level optical spectroscopy ͑DLOS͒ in an AlGaN / GaN heterostructure equivalent to that of a heterojunction field effect transistor. Band gap states were assigned to either the AlGaN or GaN regions by comparing the DLOS spectra in accumulation and pinch-off modes, where the former reflects both AlGaN-and GaN-related defects, and the latter emphasizes defects residing in the GaN. A band gap state at E c − 3.85 eV was unambiguously identified with the AlGaN region, and deep levels at E c − 2.64 eV and E c − 3.30 eV were associated with the GaN layers. Both the AlGaN and GaN layers exhibited additional deep levels with large lattice relaxation. The influence of deep levels on the two-dimensional electron gas sheet charge was estimated using a lighted capacitance-voltage method.

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“…However, from the different cross-section values one can expect that the occupation of states is different from sample to sample. We assume that the current collapse is an effect related to surface states of the AlGaN, as already shown by photoionization spectroscopy measurements where the distance between the 2DEG channel and the AlGaN surface was varied [5].…”

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confidence: 99%

Photoionization Spectroscopy of Traps in Doped and Undoped AlGaN/GaN HEMTs

Wolter

Javorka

Marso

et al. 2002

phys. stat. sol. (c)

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PACS: 71.55.Eq; 73.20.Hb; 85.30.De Deep-level defects and surface states are supposed to be responsible for the limitation of AlGaN/GaN high electron mobility transistor (HEMT) performance. In order to investigate the influence of these traps, photoionization spectroscopy was used to study doped and undoped HEMTs grown on sapphire in different metalorganic vapour-phase epitaxy reactors. This measurement technique is based on the optical reversion of the current collapse and it allows one to determine photoionization cross-sections of the participating traps. For doped and undoped HEMTs nearly the same two defect levels with excitation energies of 3.2 eV and 2.9 eV were determined. By varying the source-gate voltage it was found that the photoionization cross-section is reduced for positive gate bias, i.e. the virtual gate on the gate-drain access region is partially neutralized due to the removal of trapped electrons from surface states.

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Photo-ionization spectroscopy of traps in AlGaN/GaN high-electron mobility transistors

Cited by 10 publications

References 12 publications

Photoionization spectroscopy of deep defects responsible for current collapse in nitride-based field effect transistors

Photoionization spectroscopy of deep defects responsible for current collapse in nitride-based field effect transistors

Quantitative observation and discrimination of AlGaN- and GaN-related deep levels in AlGaN∕GaN heterostructures using capacitance deep level optical spectroscopy

Photoionization Spectroscopy of Traps in Doped and Undoped AlGaN/GaN HEMTs

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