Epitaxial Technologies for Gallium Oxide Ultra High Voltage Power Electronics
Navy STTR 2016.A - Topic N16A-T023
ONR - Ms. Dusty Lang - dusty.lang@navy.mil
Opens: January 11, 2016 - Closes: February 17, 2016

N16A-T023 TITLE: Epitaxial Technologies for Gallium Oxide Ultra High Voltage Power Electronics

TECHNOLOGY AREA(S): Electronics, Ground/Sea Vehicles, Weapons

ACQUISITION PROGRAM: PEO SHIPS: PMS 320 Electric Ships Office

OBJECTIVE: Develop gallium oxide epitaxial growth system to enable the realization of novel high voltage (greater than 20kV) power electronic switching and pulse power devices.

DESCRIPTION: Future Navy ships will require high power converters for applications such as rail gun, Air and Missile Defense Radar (AMDR), and propulsion on DDG-51 size ship platforms. High voltage, high efficiency power switches are required to achieve the needed power density. Monoclinic beta(ß)-Ga2O3 possesses a large energy bandgap of 4.8eV and high breakdown field of 8 MV/cm. These properties motivate the development of Ga2O3 for high-power/high-voltage electronic devices. Additionally, the extremely low intrinsic carrier concentration of ni = 1.8x10-22 cm-3 of Ga2O3 enables low generation/recombination rates and thus low leakage currents in a thick drift region. Theoretically, a vertical Ga2O3 device designed with a 30 µm thick n-type drift layer will operate with a 24kV breakdown. Nevertheless, the technology to produce a high-voltage Ga2O3 device structure is currently unavailable. The primary limitation is the extremely low-growth rate of current Ga2O3 epitaxy systems, e.g., metal-organic chemical vapor deposition (MOCVD). The secondary but related limitation is the controlled n-type and p-type doping of Ga2O3.

The growth of a thick, low-doped Ga2O3 drift region has proven challenging with current reactor designs. Current literature on Ga2O3 epitaxy reports growth rates on the order of a hundred nm/hour, which reasonably excludes the growth of thick drift layers. [1, 2] A key issue for Ga2O3 epitaxy is achieving a high growth rate while maintaining high epitaxial quality. A reactor technology is needed to address the specific reaction kinetics of the Ga2O3 at the gas/solid (substrate) interface as well as to minimize undesirable gas-phase nucleation that depletes the reactant supply and creates deleterious particulates. Additionally, the reactor design must enable controlled low-level (<1x1015 cm-3) n-type doping in this high-growth rate regime. In situ measurement tools can facilitate the growth of high quality Ga2O3. [3, 4]

Achieving p-type doping in Ga2O3 is difficult, which, given the similar p-type doping limitations in related metal-oxide semiconductors, is attributed to the presence of n-type vacancies formed during the growth process. The literature on n-type doping of Ga2O3 is mixed, which again may suggest that proper design of the reaction chamber is necessary to account for the specific kinetics of Ga2O3 material system. [5, 6] An optimal high-voltage power electronic device also necessitates a reactor design able to controllably deposit Ga2O3 at high n- and p- doping levels (>1x1019 cm-3). [7, 8]

Proposed growth system should meet the following thresholds:

• Deliverable Design Characteristics Value

• Controllable deposition with low-concentration (<5x1016 cm-3) n-type Ga2O3 layers

• n-type Ga2O3 with growth rates above 2 um/hr in Phase I and above 4 um/hr in Phase II

• nm-scale thickness uniformity at sub-nm RMS roughness levels

• High-concentration (>1x1019 cm-3) n-type, thin (< 50 nm) device layers

• High-concentration (>1x1018 cm-3) p-type, thin (< 50 nm) device layers

PHASE I: Determine feasibility, establish a plan, and describe the epitaxial growth tool features and issues for the design and development of a deposition system that can controllably deposit low-concentration (<1x1015 cm-3) n-type Ga2O3 layers with growth rates above 2 um/hr (>10 X current state-of-the-art). Determine the feasibility, establish a plan, and describe the epitaxial growth tool features and issues that can achieve thin (< 50nm) high-concentration (>1x1019 cm-3) n-type and p-type Ga2O3 layers and an appropriate ternary with nm-scale thickness uniformity at sub-nm RMS roughness levels. Final report should convince that the proposed product can be properly designed to address the above desired and required features and be achieved if Phase II is awarded. The small business will provide a Phase II development plan addressing technical risk reduction.

PHASE II: Develop a fully-functional epitaxy system having in situ characterization tools and capable of producing a thick, low-concentration (<5x1014 cm-3) n-type Ga2O3 drift layer (>30µm) as well as high-concentration (>5x1019 cm-3) n- and p-type doped thin (sub 100 nm) device layers within the same growth run. The system should demonstrate epitaxial growth rates of at least 4um/hr. A prototype of the fully operational system with appropriate control software will be delivered to the Navy and is required by the end of Phase II for evaluation.

PHASE III DUAL USE APPLICATIONS: Phase III shall address the commercialization of the product developed as a prototype in Phase II. The small business is expected to work with suitable industrial partners for this transition to military programs and civilian applications. The expected final state of this product will match the requirements given in Phase II and will allow for the tool to be installed, certified, and operated within standards of a modern semiconductor fabrication facility. An epitaxy system of this design will enable cost-effective semiconductor based high-power devices for solid-state transformers to replace electromagnetic transformers for the electric grid, rail traction, large-vehicle power systems, and wind turbines.

REFERENCES:

1. M. Higashiwaki, K. Sasaki, A. Kuramata, T. Masui, S. Yamakoshi, "Development of Gallium Oxide Power Devices," Physical Status Solidi Applied Material Science 211 p. 21 (2014).

2. M. Higashiwaki, K. Sasaki, A. Kuramata, T. Masui, and S. Yamakoshi, "Gallium oxide (Ga2O3) metal-semiconductor field-effect transistors on single-crystal Ga2O3 (010) substrates," Applied Physics Letters 100 013504 (2012).

3. H. Lee, K. Kim, J.Ju. Woo, D.J. Jun, Y. Park, Y. Kim, H.W. Lee, Y.J. Cho, H.M. Cho, "ALD and MOCVD of Ga2O3 Thin Films Using the New Ga Precursor Dimethylgallium Isopropoxide, Me2GaOiPr," Chemical Vapor Deposition 17 pp. 191, (2011).

4. X. Du, W. Mi, C. Luan, Z. Li, C. Xia, J. Ma, "Characterization of homoepitaxial ß-Ga2O3 films prepared by metal–organic chemical vapor deposition," Journal of Crystal Growth 404 p.75 (2014).

5. N.M. Sbrockey, T. Salagaj, E. Coleman, G.S. Tompa, Y. Moon, M. Sik, " Large-Area MOCVD Growth of Ga2O3 in a Rotating Disc Reactor," Journal of Electronic Materials Published online (2014).

6. K. Sasaki, M. Higashiwaki, A. Kuramata, T. Masui, S. Yamakoshi, Si-Ion Implantation Doping in _-Ga2O3 and Its Application to Fabrication of Low-Resistance Ohmic Contacts Applied Physics Express 6 086502 (2013).

7. D. Gogova, G. Wagner, M. Baldini, M. Schmidbauer, K. Irmscher, R. Schewski, Z. Galazka, M. Albrecht, R. Fornari, "Structural properties of Si-doped ß-Ga2O3 layers grown by MOVPE," Journal of Crystal Growth 401 pp. 665-660 (2014).

8. G. Wagner, M. Baldini, D. Gogova, M. Schmidbauer, R. Schewski, M. Albrecht, Z. Galazka, D. Klimm, R. Fornari, Homoepitaxial Growth of B-Ga2O3 layers by metal organic vapor phase epitaxy," Physica Status Solidi 211 p. 27 (2013).

KEYWORDS: Gallium Oxide, Deposition System, Wide Bandgap Semiconductor, High-Power Electronics, High Power Converters, epitaxy system

TPOC-1: Lynn Petersen

Email: lynn.j.petersen@navy.mil

TPOC-2: Fritz Kub

Email: kub@nrl.navy.mil

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