Large Area Vertical

Gallium Oxide

Schottky DiodesNeil Taylor

10/07/2020

Radiation Detection• Alpha Spectroscopy

• Reprocessing Spent Nuclear Fuel• Environmental Sampling• Health Physics• Nuclear Forensics

• Gamma Spectroscopy• Neutron Activation Analysis

• Neutron Detectors• Reactor Power• Radiation Safety• Special Nuclear Material Detection Nuclear Regulatory Commission. “Stages of the Nuclear Fuel Cycle.” Web.13 April 2019.

https://www.nrc.gov/materials/fuel-cycle-fac/stages-fuel-cycle.html

Wide Bandgap Semiconductors

Silicon Silicon Carbide

Gallium Nitride

Gallium Oxide

Bandgap (eV) 1.14 3.23 3.4 4.9

Melting Point (°C)

1,400(200)

2,730 2,500 1,800

Breakdown Voltage

(MV/cm)

0.3 ~3 ~5 ~8

Polytypes 1 >250 2 5

Commercialization

Very High High Medium Low

Cost $ $$ $$ $

2nd Generation devices

15 mm

15 mm

Processing Flow for Vertical Ga2O3

Schottky Diode (3rd)1. Wafer dicing

• Dice the wafers into 15×15 mm2

2. Ohmic Back Contact

• RCA Cleaning

• Metal deposition by E-beam: Ti /Al /Ni/Au

• Rapid Thermal Annealing

3. Passivation

• Al2O3 deposition

• SiO2 deposition

4. Top Schottky contact

• Standard photolithography process: PR Coat/Pattern/Develop

• Metal deposition by E-beam: Ni/Au

Schematic of 3rd vertical Ga2O3 Schottky diode

Ni/Au Schottky contact

n-type Ga2O3 substrate

11 μm n--Ga2O3 (n~1.4×1016 cm-3)

Ti/Al/Ni/Au ohmic contact

Al2O3/SiO2 Al2O3/SiO2

FIV Measurement

FIV Analysis

• 105 total contacts tested

• Ideality range of 1.05-1.52 with an average of 1.12

• Barrier height range of 0.81-1.13 eV with an average of 0.98 eV

IS = AART2e

−qφBKBT

I = Is(e−

qV

nKBT)

RIV Measurement

CV Measurement

CV Analysis

• 105 contacts tested

• Doping concentration: average of 1.39e16

• Barrier height average of 1.13 eV

1

𝐶2=

2

𝑞𝑁𝐷𝜀𝑠𝜀𝑜𝐴2 (𝑉𝑏𝑖 − 𝑉)

FIV Temperature

Temperature Analysis

Spectroscopy Setup

• Determine alpha spectroscopy detector capabilities

• Vacuum chamber, CAEN preamplifier, CAEN high voltage power supply, CAEN digitizer, oscilloscope, and spectroscopy software

• Alpha sources and X-ray tube

FIV Analysis

• Calculation of depletion depth based on doping of epitaxial layer

• Similar results from CV Measurement (1.43 microns at -30V)

• SRIM calculations show 5.486 MeV alpha has a 14.3 µm range in Ga2O3

Conclusions

• Successfully fabricated GaO Schottky diodes with large area contacts

• Devices operated with breakdown voltages of ~400V for 2nd

generation and ~700V for third generation

• Devices show quite linear response to temperature up to 300C

• Future generation devices can be improved through edge termination, lower background and epitaxial doping, and lower defect density

• Continued testing of devices for radiation detection both X-rays and alpha particles

Questions?

This material is based upon work partially supported by the Department of Energy / National Nuclear Security Administration under Award Number(s) DE-NA0003921.

Neil Taylor is supported by the ETI Fellowship.

Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any

agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or

usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any

specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement,

recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state

or reflect those of the United States Government or any agency thereof.

• Collaborators• Yonngchao Yu, Mihee Ji, Tolga Aytug, Ivan Kravchenko, Pooran Joshi, M.

Parans Paranthaman

• Advisor: Dr Raymond Cao