Current status of large-area MOVPE growth of HgCdTe device heterostructures for infrared focal plane arrays

Abstract

This paper reviews the current status of the growth of fully doped HgCdTe (MCT) devices by metalorganic vapor phase epitaxy (MOVPE). The current reactor system has been developed to produce 3-inch diameter epitaxial layers compatible with slice-scale processing. The new reactor system has achieved routine epitaxial growth of MCT with good morphology onto both gallium arsenide (GaAs) and GaAs on silicon (Si) wafers that were oriented (2-8°) off (100) orientation. The density of surface defects (so-called ''hillocks''), typical of MOVPE growth on such orientation substrates, has been reduced to ,5 cm ÿ 2 at a sufficient yield to make the production of low cluster defect 2D arrays possible. Alternative growth experiments onto cadmium telluride (CdTe) on Si substrates with (211)B orientation have also been performed to investigate their usefulness for infrared focal plane array (IRFPA) applications. Si substrates give better thermal expansion match to the read out Si circuits (ROIC). The horizontal reactor cell design has a graphite susceptor with a rotating platen capable of using substrates up to 4-inch diameter. Work, however, has concentrated on 3-inch diameter GaAs and GaAs on Si wafers substrates in the reactor, and these reproducibly demonstrated good compositional and thickness uniformity. Cut-off wavelength and thickness uniformity maps showed that there was sufficient uniformity to produce twelve sites of large format 2D arrays (640 3 512 diodes on 24-mm pitch) per slice. Minority carrier lifetimes in heterostructures is an important parameter and some factors affecting this are discussed, with special emphasis on As-doped material grown under various growth conditions in an attempt to reduce Shockley-Read (S-R) trap densities. New data are presented on trap densities and theoretical fitting of lifetimes in MOVPE material. Fully doped heterostructures have been grown to investigate the device performance in the 3-5 mm medium-wave IR (MWIR) band and 8-12 mm long-wave IR (LWIR). These layers have been fabricated into mesa arrays and then indium-bumped onto Si multiplexers. A summary of the 80-K device results shows that stateof-the-art device performance has been demonstrated in MOVPE-grown device structures.

As Doping in (Hg,Cd)Te: An Alternative Point of View

“…Mitra et al 27 found the As to be 15% to 50% active after a Hg vacancyfilling anneal, which increased to near 100% if a high-temperature anneal was included. More recently Maxey et al 28,29 have reported $100% activation after vacancy annealing alone. Additionally, minority carrier lifetimes comparable with Hg-rich LPE 27 were achieved.…”

“…(Me 2 N) 3 As is now the As doping precursor of choice. 28,30 It can be seen from the above that, if the As is inactive as grown, then low-temperature (200°C to 250°C) Hg-rich mercury vacancy anneals are insufficient to activate it. A Hg-rich high-temperature (400°C to 500°C) anneal followed by a vacancyfilling anneal are required and even that may not be sufficient.…”

Theoretical utmost performance of (100) mid-wave HgCdTe photodetectors

“…Several approaches to prevent hillocks creation have been tried: zinc nucleation layer, different Cd/Te ratios, different substrates orientations have been used, but we were not able to grow hillocks-free layer in controllable way on GaAs substrates. According to literature, only Selex Galileo reported on suppression of hillocks density below 5 cm -2 in the (100) HgCdTe grown on GaAs (Maxey et al 2000(Maxey et al , 2006. Therefore, most of our reported MWIR HgCdTe N ?…”

Electrical properties of HgCdTe films grown by MOCVD and doped with as

“…The growth process was optimized for photoelec− tronic devices operating at near−room temperature. Typi− cally, (111)B HgCdTe layers are grown on (100) GaAs with 3 deg off <110> orientation, which is enforced with suitable growth condition [7]. The (111) growth is characterized by important advantages, as it proceeds faster, provides hill− ock−free surface and ensures more efficient iodine doping with low precursor concentration [8].…”