AlGaN/GaN heterojunction bipolar transistor structures-design considerations

Cai, C.; Ruden, P. P.

doi:10.1063/1.373778

Cited by 12 publications

(5 citation statements)

References 51 publications

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“…With this goal in mind, quite a few researchers are working to develop GaN-based heterojunction bipolar transistors (HBTs). [4][5][6][7][8][9] Although results thus far have been promising, there are still a number of outstanding materials issues. For example, AlGaN-GaN HBTs appear to be limited by large acceptor ionization energies and low hole mobilities.…”

Section: Introductionmentioning

confidence: 99%

“…For example, AlGaN-GaN HBTs appear to be limited by large acceptor ionization energies and low hole mobilities. 4 We describe the use of wafer fusion to form HBTs with an AlGaAs-GaAs emitter-base and a GaN collector. In this way, we hope to make use of both the high breakdown voltage of the GaN and the high mobility of the technologically more mature GaAs-based materials.…”

Section: Introductionmentioning

confidence: 99%

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Wafer-fused n-AlGaAs/p-GaAs/n-GaN Heterojunction Bipolar Transistor with uid-GaAs Base-Collector Setback

et al. 2003

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Recently we reported the first AlGaAs-GaAs-GaN heterojunction bipolar transistor (HBT), a device that potentially combines the high-breakdown voltage of an n-GaN collector with the high mobility of an AlGaAs-GaAs emitter-base. Because of the high degree of lattice mismatch between GaAs (lattice constant of 5.65A) and GaN (3.19A), we formed these devices through wafer fusion, also called direct wafer bonding. Measurements on the first generations of wafer fused HBTs revealed good current modulation, with modest output current (0.83 KA/cm2) and a current gain of 1.2. Limitations to the current gain may be related to traps and defects introduced by the fusion process, or may be a consequence of the natural conduction band offset between GaAs and GaN, which is not well known. This paper describes our new HBT structure that included a thin (20nm) uid-GaAs base-collector “setback” layer. The setback layer shifted the fused GaAs-GaN interface slightly into the collector. This new HBT structure also incorporated a reduced base thickness of 100 nm. HBTs with setback layers demonstrate increased output current (1.7 KA/cm2) and increased current gain (1.9).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Wafer-fused n-AlGaAs/p-GaAs/n-GaN Heterojunction Bipolar Transistor with uid-GaAs Base-Collector Setback

et al. 2003

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“…A relatively conservative value for the hole mobility is 10cm 2 /Vs [9]. To make full use of the polarization charge effect and to avoid lattice relaxation a complex device structure is designed [10]; the parameters are summarized in Table I. Fig.…”

Section: Hbt Design For Low Base Resistancementioning

confidence: 99%

Current Gain of an AlGaN/GaN Heterojunction Bipolar Transistor

Ruden

2001

MRS Proc.

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A novel hybrid model and simulation results for an advanced, graded base AlGaN/GaN heterojunction bipolar transistor structure are presented. The base of the n-p-n HBT examined has two parts, a linearly graded AlGaN layer on the emitter side and a heavily p-doped GaN layer on the collector side. In the hybrid model developed here the potential profile is first calculated self-consistently in the biased state taking into account ionized impurity charges, polarization charges, and majority carrier charges. The minority carrier transport is examined subsequently. Injection of electrons from the emitter is modeled as a thermionic emission process. The minority electron transport process in the graded region is drift-dominated due to the large built-in effective field strength. In the low-field GaN layer of the base, electron transport is assumed to be diffusion-dominated. High-level injection effects are modeled in the framework of the Gummel-Poon model. Example structure design parameters are presented and it is found that the calculated current gain can be greater than 25, with a collector current density of 10 4 A/cm 2 .

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“…Unlike AlGaN/GaN high electron mobility transistors (HEMTs) which have witnessed rapid development, GaN based heterojunction bipolar transistors (HBTs) have been seriously plagued by the highly resistive p-type base and metal/p-GaN ohmic contacts [1,2]. To borrow another suitable material for the base, AlGaAs/GaAs is a promising candidate which has high electron injection efficiency, highly conductive p-type base, and short base transit time.…”

Section: Introductionmentioning

confidence: 99%

The role of setback layers on the breakdown characteristics of AlGaAs/GaAs/GaN HBTs

Lian

Xing

2008

Phys. Status Solidi (c)

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Breakdown voltages (VCBO) of AlGaAs/GaAs/GaAs and AlGaAs/GaAs/GaAs‐setback/GaN HBTs have been compared both theoretically and experimentally with respect to setback layer thicknesses and the doping type. VCBO was calculated using a non‐local energy model. The hard breakdown voltage was measured on as‐grown GaAs homojunctions and AlGaAs/GaAs/GaN HBTs formed by direct wafer fusion. The calculation showed an increase of VCBO from ∼ 20 V to ∼ 325 V by replacing the GaAs collector with GaN, and VCBO ∼90 V was indeed measured. The smaller than predicted VCBO is attributed to the large leakage current currently present in the fused junctions. Insertion of a lightly doped GaAs setback layer has resulted in improved current gain of the fused HBTs, but it also degrades the breakdown characteristics. 20‐30 nm setback layers were found to maintain VCBO significantly higher than that of GaAs homojunctions and likely reasonable current gains. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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AlGaN/GaN heterojunction bipolar transistor structures-design considerations

Cited by 12 publications

References 51 publications

Wafer-fused n-AlGaAs/p-GaAs/n-GaN Heterojunction Bipolar Transistor with uid-GaAs Base-Collector Setback

Wafer-fused n-AlGaAs/p-GaAs/n-GaN Heterojunction Bipolar Transistor with uid-GaAs Base-Collector Setback

Current Gain of an AlGaN/GaN Heterojunction Bipolar Transistor

The role of setback layers on the breakdown characteristics of AlGaAs/GaAs/GaN HBTs

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