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

Armstrong, Andrew M.; Chakraborty, Arpan; Speck, James S.; DenBaars, Steven P.; Mishra, Umesh K.; Ringel, S. A.

doi:10.1063/1.2424670

Cited by 38 publications

(27 citation statements)

References 12 publications

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“…The E C -3.25 has been previously reported to be a GaN buffer trap that correlates with the presence of residual carbon manifesting as C N substitutional defects [14][15][16]. The E C -3.8 eV, simply by virtue of its activation energy being larger than the GaN bandgap, must be an AlGaN trap, and has been reported previously [17]. On-resistance data collected from DC output IV of the GaN HEMT before and after stress in the dark, with 1.2 eV, and with 3 eV monochromatic light shining on the GaN HEMT.…”

Section: Resultsmentioning

confidence: 86%

Identification of an RF degradation mechanism in GaN based HEMTs triggered by midgap traps

Sasikumar

Arehart

Via

et al. 2015

Microelectronics Reliability

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Quantitative defect spectroscopy was performed on low gate leakage operational S-band GaN HEMTs before and after RF accelerated life testing (ALT) to investigate and quantify potential connections between the evolution of observed traps and RF output power loss in these HEMTs after stressing. Constant drain current deep level transient spectroscopy and deep level optical spectroscopy (CI D -DLTS and CI D -DLOS, respectively) were used to interrogate thermally-emitting traps (CI D -DLTS) and deeper optically-stimulated traps (CI D -DLOS) so that the entire bandgap can be probed systematically before and after ALT. Using drain-controlled CI D -DLTS/DLOS, with which traps in the drain access region are resolved, it is found that an increase in the concentration of a broad range of deep states between E C -1.6 to 3.0 eV, detected by CI D -DLOS, causes a persistent increase in on-resistance of 0.22 Ω-mm, which is a likely source for the 1.2 dB reduction in RF output power that was observed after stressing. In contrast, the combined effect of the upper bandgap states at E C -0.57 and E C -0.72 eV, observed by CI D -DLTS, is responsible for only~10% of the on-resistance increase. These results demonstrate the importance of discriminating between traps throughout the entire bandgap with regard to the relative roles of individual traps on degradation of GaN HEMTs after ALT.

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Section: Resultsmentioning

confidence: 86%

Identification of an RF degradation mechanism in GaN based HEMTs triggered by midgap traps

Sasikumar

Arehart

Via

et al. 2015

Microelectronics Reliability

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“…Early studies revealed that gate lag and drain current collapse in HFET devices were related to traps in the AlGaN surface and GaN buffer layers. 1 Many techniques, such as photoionization spectroscopy, 2 deep level transient spectroscopy ͑DLTS͒, 3 deep level optical spectroscopy ͑DLOS͒, 4,5 and current-DLTS on HFETs, 6 have been used to study traps in AlGaN/GaN structures. Carbon is a common residual impurity in unintentionally doped ͑UID͒ GaN buffer layers grown by metalorganic chemical vapor deposition ͑MOCVD͒ but the carbon concentration and resistivity in these layers can be controlled by growth pressure.…”

Section: Introductionmentioning

confidence: 99%

Deep traps in AlGaN/GaN heterostructures studied by deep level transient spectroscopy: Effect of carbon concentration in GaN buffer layers

Fang

Claflin

Look

et al. 2010

Journal of Applied Physics

101

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Electrical properties, including leakage currents, threshold voltages, and deep traps, of AlGaN/GaN heterostructure wafers with different concentrations of carbon in the GaN buffer layer, have been investigated by temperature dependent current-voltage and capacitance-voltage measurements and deep level transient spectroscopy ͑DLTS͒, using Schottky barrier diodes ͑SBDs͒. It is found that ͑i͒ SBDs fabricated on the wafers with GaN buffer layers containing a low concentration of carbon ͑low-͓C͔ SBD͒ or a high concentration of carbon ͑high-͓C͔ SBD͒ have similar low leakage currents even at 500 K; and ͑ii͒ the low-͓C͔ SBD exhibits a larger ͑negative͒ threshold voltage than the high-͓C͔ SBD. Detailed DLTS measurements on the two SBDs show that ͑i͒ different trap species are seen in the two SBDs: electron traps A x ͑0.9 eV͒, A 1 ͑0.99 eV͒, and A 2 ͑1.2 eV͒, and a holelike trap H 1 ͑1.24 eV͒ in the low-͓C͔ SBD; and electron traps A 1 , A 2 , and A 3 ͑ϳ1.3 eV͒, and a holelike trap H 2 ͑Ͼ1.3 eV͒ in the high-͓C͔ SBD; ͑ii͒ for both SDBs, in the region close to GaN buffer layer, only electron traps can be detected, while in the AlGaN/GaN interface region, significant holelike traps appear; and iii͒ all of the deep traps show a strong dependence of the DLTS signal on filling pulse width, which indicates they are associated with extended defects, such as threading dislocations. However, the overall density of electron traps is lower in the low-͓C͔ SBD than in the high-͓C͔ SBD. The different traps observed in the two SBDs are thought to be mainly related to differences in microstructure ͑grain size and threading dislocation density͒ of GaN buffer layers grown at different pressures.

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“…3 Although photoluminescence ͑PL͒ or cathodoluminescence ͑CL͒ investigation has shown some characteristic luminescence peaks related to deep electronic levels in AlGaN and AlN, 3-7 electrical characterization on deep levels in AlGaN or AlGaN/GaN heterostructure has been reported only a few times. [8][9][10][11] In particular, the deep-level transient spectroscopy ͑DLTS͒ method only detected deep levels with activation energies under 0.9 eV, 10 in spite of the fact that a near-midgap level can act as a dominant recombination center rather than a level near conduction or valence band. To detect near-midgap levels in AlGaN, a temperature range should extend to 800 K in a typical DLTS measurement condition.…”

mentioning

confidence: 99%

Near-midgap deep levels in Al0.26Ga0.74N grown by metal-organic chemical vapor deposition

Sugawara

Kotani

Hashizume

2009

Applied Physics Letters

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A deep level with an activation energy of 1.0 eV in n-type Al 0.26 Ga 0.74 N grown by metal-organic chemical vapor deposition was detected by deep-level transient spectroscopy ͑DLTS͒ with a sampling time window of several seconds. The deep-level density was 6 ϫ 10 15 cm −3 . At the temperatures around which the DLTS peaks were observed, capacitance transient was measured. Under the dark condition, a capacitance increase was observed, corresponding to the thermal emission of electrons from the level with 1.0 eV activation energy. After that, we observed a large capacitance increase under illumination with 2.3 eV photon energy. On the basis of potential simulation taking account of deep levels, we found that the photoinduced capacitance change arose from electron emission from additional near-midgap levels in energy ranging from E C − 1.5 to E C − 2. Deep levels in AlGaN induce not only serious degradation, such as drain current instability and lack of long-term reliability, in AlGaN/GaN-based transistors 1,2 but also significant reduction in light-emitting efficiency in ultraviolet light-emitting diodes and laser diodes using AlGaN materials. 3 Although photoluminescence ͑PL͒ or cathodoluminescence ͑CL͒ investigation has shown some characteristic luminescence peaks related to deep electronic levels in AlGaN and AlN, 3-7 electrical characterization on deep levels in AlGaN or AlGaN/GaN heterostructure has been reported only a few times. [8][9][10][11] In particular, the deep-level transient spectroscopy ͑DLTS͒ method only detected deep levels with activation energies under 0.9 eV, 10 in spite of the fact that a near-midgap level can act as a dominant recombination center rather than a level near conduction or valence band. To detect near-midgap levels in AlGaN, a temperature range should extend to 800 K in a typical DLTS measurement condition. In such very high temperatures, a Schottky or a p-n junction suffers from serious leakage and thermal junction breakdown. In this letter, we characterize near-midgap deep levels in AlGaN grown by metal-organic chemical vapor deposition ͑MOCVD͒ using a combination of DLTS and photoassisted capacitance transient methods.We used a Si-doped n-Al 0.26 Ga 0.74 N layer with a thickness of 1.0 m grown at 1000°C on a sapphire substrate by MOCVD. Hall measurements determined the typical values of electron concentration and mobility of the AlGaN layer at room temperature ͑RT͒ to be 2 ϫ 10 17 cm −3 and 100 cm 2 / V s, respectively. As a ring-shaped Ohmic contact, a Ti/Al/Ti/Au multilayer structure ͑20/50/20/150 nm͒ was deposited on the AlGaN surface, followed by an annealing at 800°C for 1 min in N 2 ambient. A circular Schottky electrode with a diameter of 200 m was fabricated at the center of the Ohmic ring by an electron-beam deposition of Ni.To try to detect deep levels with large activation energies in a temperature range as low as possible in the DLTS measurement, a time window of up to several seconds was used with an optimized signal sampling system and a temperaturesweeping rate...

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

Cited by 38 publications

References 12 publications

Identification of an RF degradation mechanism in GaN based HEMTs triggered by midgap traps

Identification of an RF degradation mechanism in GaN based HEMTs triggered by midgap traps

Deep traps in AlGaN/GaN heterostructures studied by deep level transient spectroscopy: Effect of carbon concentration in GaN buffer layers

Near-midgap deep levels in Al0.26Ga0.74N grown by metal-organic chemical vapor deposition

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