Experimental Investigation of of the use of Elemental Transmutation for efficient p-type doping in

HgCdTe and HgCdTeSeContract Officer: Dr. W. Clark, Army Research Office

Contract Period 8/15/01 – 8/14/04

PI’s: T.D. Golding and C.L. Littler, University of North Texas

Dr. J.H. Dinan, US Army CECOM NVESD, Fort Belvoir

J.A. Dura, R.M. Lindstrom, NIST, Gaithersburg, MD

H.F. Schaake , DRS Infrared Technologies, Dallas, TX

In collaboration with

● Control of p-type doping processes in HgCdTe is a prerequisite to fabricate high performance infrared detector devices.

● Group I elements such as Li, Cu, Ag, and Au are readily incorporated into metallic sites giving p-type activity, their high diffusion coefficients restrict their use in advanced devices. l Group V element As is preferred as a p-dopant because it has a low diffusivity.

● However, As is amphoteric within the HgCdTe lattice, occupying both metal and nonmetal sites, giving donor and acceptor characteristics respectively.

● Requires complex deposition and annealing schemes to give p-type behavior.

Rational

● Two techniques are being studied for incorporating As into HgCdTe that should ensure its presence only on nonmetal sites.  

● Based on the fact that Se can be readily incorporated into group VI sites and that 75Se naturally decays into 75As.  

Since the nuclear recoils associated with this decay are too small to displace arsenic atoms, substitutional p-doping should be ensured.  

● Method (I): Transmutation Doping (TD)Isotopically pure or isotopically enhanced 75Se can be incorporated onto nonmetal sites in

HgCdTe at dopant-concentration levels. 75Se subsequently decays to As.

● Method (II):Neutron Transmutation Doping (NTD)   A HgCdTe74Se quaternary alloy epilayer with low Se content (< 1%) can be exposed to a thermal neutron flux, transmuting the stable 74Se isotope into unstable 75Se via neutron capture. As in Method I, 75Se subsequently decays to As.

Rational (cont.)

Progress to dateMagneto-transport measurementsEffects of neutron irradiation on transport properties Magneto-conductivity tensor analysis of Hall anomalous transport effects (two-electron model)

Future WorkSe incorporation in LPE HgCdTeTransport and Magneto-Optics

“Nominally undoped HgCdTe epilayers will be supplied for this program by the US Army Night Vision Laboratories, and DRS Infrared…”

40 samples of LPE HgCdTe supplied to UNT by DRS: 10 samples of MBE HgCdTe supplied to UNT by NVEOL

”The control samples will be fully characterized at UNT by temperature dependent magnetotransport and magneto-optics to determine carrier levels, mobilties, compensation and defect levels…”

5 of control samples characterized by temperature-dependent magnetotransport. Concentrations, mobilities, and transport mechanisms determined for these samples.

“The HgCdTe alloys will be irradiated in a thermal neutron flux using the reactor facilities at the National Institute for Standards and Technology…”

5 of samples irradiated and characterized by temperature-dependent magnetotransport. Effects of irradiation on the properties of HgCdTe determined.

“The test samples will be characterized by SIMS to determine dopant (Se and As) profiles…”

2 samples implanted with As and Se (2 x 1014 cm-3)

Samples currently at DRS Infrared for activation anneal

0.1 1 10-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Con

duct

ivity

xy

(1/

cm

)

Magnetic field (kG)

Experimental Resultsn1 = 1.47 x 1014 cm-3

μ1 = 7.52 x 104 cm2/V.s

n2 = 1.85 x 1014 cm-3

μ2 = 2.67 x 104 cm2/V.s

Two Carrier Fit