Impact of GaN cap thickness on optical, electrical, and device properties in AlGaN/GaN high electron mobility transistor structures

Waltereit, Patrick; Müller, Stefan; Bellmann, Konrad; Buchheim, C.; Goldhahn, R.; Köhler, K.; Kirste, Lutz; Baeumler, M.; Dammann, M.; Bronner, W.; Quay, R.; Ambacher, O.

doi:10.1063/1.3184348

Cited by 42 publications

(25 citation statements)

References 22 publications

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“…Some improvements of AlGaN/GaN HEMTs in device performance, reliability and reproducibility were also seen in the HEMT epitaxial structures capped by a thin GaN layer [87]. Ponky Ivo et al reported that the robustness of AlGaN/GaN HEMTs under high DC stress was significantly improved by adding a thin GaN cap [88].…”

Section: Surface Passivationmentioning

confidence: 97%

MOCVD growth of GaN-based high electron mobility transistor structures

Chen¹

2015

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IICover: surface morphology of a GaN high electron mobility transistor structure grown on a native GaN substrate. The image was obtained with an atomic force microscope. AbstractWide bandgap group-III nitride semiconductors like GaN, AlN, and their alloys are very suitable for the use in high-power, high-frequency electronics, as a result of their superior intrinsic properties. The polarization-induced high-density and high-mobility two-dimensional electron gas (2DEG) forming in (0001) oriented AlGaN/GaN heterostructures enable the epitaxial structure to be utilized for high electron mobility transistors (HEMTs). Outstanding power handling and record high frequency have been demonstrated from GaN-based HEMT devices over time. However, the shortterm stability and the long-term reliability of the device performances remain problematic. In order to make GaN HEMT technology truly take off and breach the civilian market like automotive, telecommunication applications, the problems need to be solved to justify its relatively high cost over the solutions based on Si and GaAs technologies.At the material level, there are two major challenges; one is the reduction of highdensity structural defects in heteroepitaxially grown layers when foreign substrates are used, and the other is the control of "deep" electron traps forming in the middle of the "wide" bandgap by intrinsic defects or extrinsic impurities.The main idea of the present work was therefore to tackle these material issues directly, using an approach called bottom-to-top optimization to improve the overall quality of GaN-based HEMT epitaxial structures grown on semi-insulating (SI) SiC and native GaN substrates. The bottom-to-top optimization means an entire growth process optimization, from in-situ substrate pretreatment to the epitaxial growth and then the cooling process. Great effort was put to gain the understanding of the influence of growth parameters on material properties and consequently to establish an advanced and reproducible growth process. Many state-of-the-art material properties of GaNbased HEMT structures were achieved in this work, including superior structural integrity of AlN nucleation layers for ultra-low thermal boundary resistance, excellent control of residual impurities, outstanding and nearly-perfect crystalline quality of GaN epilayers grown on SiC and native GaN substrates, respectively, and record-high room temperature 2DEG mobility obtained in simple AlGaN/GaN heterostructures.The epitaxial growth of the wide bandgap III-nitride epilayers like GaN, AlN, AlGaN, and InAlN, as well as various GaN-based HEMT structures was all carried out in a hot-wall metalorganic chemical vapor deposition (MOCVD) system. A variety of structural and electrical characterizations were routinely used to provide fast feedback VI for adjusting growth parameters and developing improved growth processes, such as optical microscopy (OM), atomic force microscopy (AFM), x-ray diffraction (XRD), capacitance-voltage measurement (CV) as well as sheet resistance...

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Section: Surface Passivationmentioning

confidence: 97%

MOCVD growth of GaN-based high electron mobility transistor structures

Chen¹

2015

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“…From self-consistent Poisson Schrödinger calculations [7] we expect a slight decrease in carrier density with increasing GaN cap layer thickness under the assumption of a constant surface potential independent of cap layer thickness. In order to understand this discrepancy between experimental and theoretical dependence of the sheet carrier concentration on GaN cap layer thickness we have performed electro-optical measurements on our samples [8]. Table 1 lists the results for electric field strengths and the surface potential.…”

Section: Impact Of Gan Cap Thicknessmentioning

confidence: 97%

Development of rugged 2 GHz power bars delivering more than 100 W and 60% power added efficiency

Waltereit¹,

Bronner

Quay

et al. 2010

Phys. Status Solidi (c)

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In this work we systematically study the structural, optical and electrical properties of AlGaN/GaN heterostructures grown by MOCVD 3-inch on SiC substrates Thefinally developed HEMTs demonstrate excellent highvoltage stability, high power performance and large power added efficiencies. For a drain bias of 100 V an output-power-density around 26 W/mm with 25 dB linear gain is obtained. On 36 mm gate width devices an output power beyond 100 W is achieved with a power added efficiency above 60% and a linear gain around 17 dB. Ruggedness on these large devices is proven by successfully passing harsh intentional device mismatch tests during operation at 50 V. Reliability is tested at a drain bias of 50 V. Under DC conditions a drain-current degradation below 20% after 20 years is extrapolated. Under RF stress the observed change in output power is well below 0.1 dB after a test duration of more than 500h

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“…The latter consists of an AlGaN barrier layer and a thin GaN cap. Our standard AlGaN thickness is 22 nm, the GaN cap has a thickness of 3 nm [3]. Processing is based on standard III-V equipment using stepper lithography for dimensions above 400 nm and e-beam lithography for smaller dimensions.…”

Section: Epitaxial Growth and Processingmentioning

confidence: 99%

Trade‐offs between performance and reliability in AlGaN/GaN transistors

Waltereit

Bronner

Quay

et al. 2011

Phys. Status Solidi C

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We report on the trade-off between performance and reliability for AlGaN/GaN transistors. It is shown that changes in epitaxial growth, transistor design and process may lead to an improvement in performance but are, at the same time, accompanied by a degradation of device reliability. As a result we show strategies in order to balance performance and reliability as both are linked. Based on these findings we have realized state-of-the-art power bars for mobile communication systems and X-band MMICs for radar applications

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Impact of GaN cap thickness on optical, electrical, and device properties in AlGaN/GaN high electron mobility transistor structures

Cited by 42 publications

References 22 publications

MOCVD growth of GaN-based high electron mobility transistor structures

MOCVD growth of GaN-based high electron mobility transistor structures

Development of rugged 2 GHz power bars delivering more than 100 W and 60% power added efficiency

Trade‐offs between performance and reliability in AlGaN/GaN transistors

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