MBE HgCdTe heterostructure detectors

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N91-14402 Innovative Long Wavelength- Infrared Detector Workshop Pasadena, April 1990

MBE HgCdTe Heterostructure Detectors J.N. Schulman and O.K. Wu Hughes Research Laboratories 3011 Malibu Canyon Road Malibu, CA 90265 HgCdTe has been the mainstay for medium (3-5/im) and long (10-14//m) wavelength infrared detectors in recent years. Conventional growth and processing techniques are continuing to improve the material. However, the additional ability to tailor composition and placement of doped layers on the tens of angstroms scale using MBE provides the opportunity for new device physics and concepts to be utilized. MBE-based device structures to be discussed here can be grouped into two categories: tailored conventional structures and quantum structures. The tailored conventional structures are improvements on familiar devices, but make use of the ability to create layers of varying composition and thus band gap at will. The heterostucture junction can be positioned independently of doping p-n junctions. This allows the small band gap region in which the absorption occurs to be separated from a larger band gap region in which the electric field is large and where unwanted tunneling can occur. Data from hybrid MBE/LPE/bulk structures will be shown. Quantum structures include the Hg-Te-CdTe superlattice, in which the band gap and transport can be controlled by alternating thin layers (tens of angstroms thick) of HgTe and CdTe. The superlattice has been shown to exhibit behavior which is non-alloy like, including very high hole mobilities, two-dimensional structure in the absorption coefficient, resonant tunneling, and anisotropic transport.

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MBE HgCdTe HETEROSTRUCTURE DETECTORS J.N. SCHULMAN and O.K. WU HUGHES RESEARCH LABORATORIES 3011 Malibu Canyon Road Malibu,CA 90265

HUGHES

QUANTUM / CLASSICAL STRUCTURES Quant/urn effect/ structure Super lattice - New material

properties.

A. B.

Layer thickness tai l o r a b l e band gaps Enhanced effective masses / reduced tunneI i ng.

C.

New phys i cs 1. H i g h ho Ie mob i I i t i es 2. 2-D density of states 3. Intrinsic interface states 352

QUANTUM / CLASSICAL STRUCTURES II. "Classical Devices 11 A. Doping profi le control. B. Composition p r o f i l e control. C. Carrier generation / c o l l e c t i o n regions separated. D. Hybrid devices - diodes, transistors, s i g n a l processing, lasers.

An MBE GROWN MULTILAYER STRUCTURE (In DOPED & UNDOPED)

HUGHES

0.8 jim

Hga? Cd asTe UNDOPED Hg 0.7Cd 0.3 Te In DOPED

800°C

0.8 |im

Hg 0 7 Cd 0 3 Te In DOPED

700°C

0.8 jim

Hg0.7Cd0.3Te In DOPED

600°C

0.8 jam

Hg 0.7 Cd 0.3Te UNDOPED

0.8 jim

CdTe BUFFER

0.8

CdTe SUBSTRATE

353

102°

HUGHES

9023-09-01

SIMS PROFILE OF AN n TYPE (IN DOPED) MBE GROWN HgCdTe MULTILAYER (5) STRUCTURE

2

3

4

DEPTH (MICRONS)

A HYBRID p-on-n HETEROJUNCTION STRUCTURES

H

9 0.7 Cd o.3Te

H

Cd

9o.8 o.2

Te

As DOPED, 5x10 16 /cm 3 MBE GROWN, 2 jim In DOPED, 5x10 1 4 /cm 3 BULK GROWN 354

RELATIVE SPECTRAL RESPONSE OF p-on-n HETEROJUNCTION DIODES

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HUGHES

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V1658-3EDIODE977K AVERAGE CUTOFF 11.76 ±0.08

z o

5 en o Q. W HI DC

0.1 UJ DC

1 2 3 4

5 6 7 8 9 10 11 WAVELENGTH (n«n)

12 13 14 15

MBE p ON n DLHJ WAFERS

HUGHES

CM

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MBE TECHNOLOGY PROVIDES EXCELLENT P+-N HETEROJUNCTIQN CHARACTERISTIC 8 x 9 MIL TFST n.nnco yi658-B3/SW611H/MCT 204H ,8 x 9 MIL TEST DIODFS MRF p ON-n. AFTER CdTe PA.