Investigations of Cd Te and Cd Zn Te crystals

Investigations of Cd. Te and (Cd, Zn)Te crystals grown by the Bridgman method M. Fiederle, A. Fauler, V. Babentsov, J. Franc, J. Ludwig, K. W. Benz Freiburger Materialforschungszentrum FMF Albert-Ludwigs-Universität Stefan-Meier-Straße 21, D-79104 Freiburg www. 2 -6. uni-freiburg. de; Email: michael. fiederle@fmf. uni-freiburg. de • growth of 25 and 75 mm Cd. Te • defects and compensation • material properties and detector performance Freiburger Materialforschungszentrum FMF M. Fiederle

Why is doping of Cd. Te/(Cd, Zn)Te necessary? • there are three posibilities to obtain high resistivity: – intrinsic material (problem of shallow impurities) – shallow compensation (problem of stability) • Cl, In, . . . – three level compensation • deep intrinsic defect (Te. Cd, VCd, ? ? ) • deep donor – V, Ge, Fe, . . . (problem of deep traps) • doping is mandatory to obtain high resistivity! Freiburger Materialforschungszentrum FMF M. Fiederle

configuration of growth • ampoule – inner diameter 24 and 75 mm – semiconductor quality HSQ 300 / HSQ 800 Heraeus – graphitized ampoule • furnace – ceramic tube (safety) – 4 Pt. Rh-Pt thermocouples – online monitoring (4 values / 10 sec. ) • material – 7 N Cd, Te, Zn (6 N) – dopants: Ge, Sn, Al, In, Cl – C[dopants]: 1018 - 1019 Freiburger Materialforschungszentrum FMF M. Fiederle

temperature timeline 75 mm Cd. Te melting point Cd. Te exothermic reaction (400 K in 10 sec) melting Cd and Te Freiburger Materialforschungszentrum FMF M. Fiederle

(Cd, Zn)Te undoped crystal 24 mm Freiburger Materialforschungszentrum FMF M. Fiederle

grains and twins – problems of melt growth Cd. Te: Ge wafer grown with modifications Freiburger Materialforschungszentrum FMF M. Fiederle

resistivity of 75 mm Cd. Te: Ge wafer (TDCM) axial distribution: 2. 0 – 8. 0 x 109 Wcm Freiburger Materialforschungszentrum FMF M. Fiederle

chemical analysis GDSM and LIMS cooperation with R. James, Brookhaven National Lab. and E. Cross, Sandia National Labs. • • • concentration of impurties in ppm GDMS data of three different locations of Cd. Te: Ge crystal concentration of Ge (AAS): – 2 – 3 x 1016 cm-3 total concentration of shallow impurities less than 3 ppm (~ 4 x 1016 cm-3) concentration of possible deep level: – Fe 47 ppb (~ 7 x 1014 cm-3) Freiburger Materialforschungszentrum FMF M. Fiederle

deep levels in Cd. Te: Ge Freiburger Materialforschungszentrum FMF M. Fiederle

Freiburger Materialforschungszentrum FMF M. Fiederle

Resistivity and PL signal of undoped (Cd, Zn)Te PL map at 80 K Resistivity map at RT ( h nmax = 1. 636 e. V ) 1 E 10 3, 000 7 E 9 25 5, 5 E 9 20 4 E 9 15 2, 5 E 9 10 25 Resistivity ( W cm) 30 Crystal length (mm) 30 8, 5 E 9 2, 449 20 1, 760 15 10 1, 209 5 1 E 9 5 0 5 10 15 20 25 Crystal diameter (mm) 30 0, 6578 0 0 5 10 15 20 Crystal diameter (mm) Freiburger Materialforschungszentrum FMF M. Fiederle PL Intensity in pseudo-colors 35

Detektor properties • Setup: – Amptek A 250 Preamplifier – module with bonded detector – detector with guarding properties (alpha particles) detector me t e t. b. measured (10 -4 cm 2/V) m ht h 6 x 10 -5 cm 2/V resolution bias Freiburger Materialforschungszentrum FMF 10 % 30 – 200 V M. Fiederle

technolgy • detector processing – lithography – metalization – wire bonding – passivation (BCB) • fabrication of strip detectors – 127 µm pitch – 24 x 14 mm detector array 14 x 24 mm detection area Freiburger Materialforschungszentrum FMF M. Fiederle

Photocurrent a. u. X-ray analysis of a copper-cable ( 500 µm diameter) X [mm] ©Sikora Industrieelektronik Gmb. H Freiburger Materialforschungszentrum FMF M. Fiederle

Technology: Flip Chip Bonding Cd. Te • cooperation with Prof. G. Anton, H. Braml Friedrich-Alexander-Universität Erlangen-Nürnberg • in-house processing of Cd. Te and (Cd, Zn)Te Quelle: Pac Tech Freiburger Materialforschungszentrum FMF M. Fiederle

Technology: Flip Chip Bonding Cd. Te • technology: Solder bumps • material: Pb. Sn and In • processing: Electroplating (Cu+Pb. Sn) Deposition (Indium) • backend: manual Flip-Chip-Bonding Freiburger Materialforschungszentrum FMF M. Fiederle

Summary • successful growth of 75 mm and 24 mm Cd. Te and (Cd, Zn)Te – large single crystalline areas • high resistivity material (>5 x 109 Wcm) – successful compensation by • deep donor Ge, Sn and undoped (Cd, Zn)Te – homogeneous distribution of material properties – deep levels correlated with Ge, Fe and Cu were detected • detector performance suffient – reduction of impurities / dopants necessary • successful detector technology – pixel detectors under developing Freiburger Materialforschungszentrum FMF Acknowledgement: • European Space Agency – MAP programm • Humboldt Stiftung M. Fiederle

compensation in Cd. Te: Ge • 3 level compensation – shallow acceptor NA(Cu, . . . ) – shallow donor ND(Cl, In, . . ) – deep donor NDD • germanium Freiburger Materialforschungszentrum FMF M. Fiederle

compensation in Cd. Te: Ge • 3 level compensation – shallow acceptor NA(Cu, . . . ) – shallow donor ND(Cl, In, . . ) – deep donor NDD • germanium Freiburger Materialforschungszentrum FMF M. Fiederle

photoluminescence of Cd. Te: Ge • mapping of 45 mm wafer • selection of different energy levels corresponding to: – A-center – exciton – deep level at 1. 0 e. V • comparison with resitivity mapping Freiburger Materialforschungszentrum FMF M. Fiederle

Comparison resistivity and photosensitivity Freiburger Materialforschungszentrum FMF M. Fiederle

photoluminescence spectra (77 K) of Cd. Te: Ge • found emissions: – near band gap emmision (FE) – A-center – 1. 1 e. V emission – 0. 82 e. V • slightly reduction of crystal quality from beginning of growth to the end Freiburger Materialforschungszentrum FMF M. Fiederle

growth of 25 mm (Cd, Zn)Te • • • ampoule – inner diameter 24 mm – semiconductor quality HSQ 800 Heraeus – graphitized ampoule furnace – ceramic tube (safety) – 4 Pt. Rh-Pt thermocouples – online monitoring (4 values / 10 sec. ) material – 7 N Cd, Te – 6 N Zn – 5 percent Zn Freiburger Materialforschungszentrum FMF M. Fiederle

Freiburger Materialforschungszentrum FMF M. Fiederle

Resistivity and Zn concentration • strong correlation between zinc concentration and resistivity 5, 2 Zn (at. %) 4, 8 • resistivity and zinc show the same behaviour 4, 4 a 4, 0 3, 6 3, 2 10 2, 0 x 10 r (W cm) • experimental data close to theoretical ones 1 10 1, 6 x 10 theoretical 10 1, 2 x 10 9 8, 0 x 10 2 9 4, 0 x 10 0, 0 0 5 10 15 20 X (mm) Freiburger Materialforschungszentrum FMF M. Fiederle 25

zinc concentration in the lower part y (mm) 10 zn 1 4, 444 8 4, 089 6 4 3, 733 Zn (at. %) 4, 800 2 2 4 6 8 10 12 14 16 18 20 22 24 3, 378 x (mm) Freiburger Materialforschungszentrum FMF M. Fiederle

deep levels in Cd. Te: Ge Conduction band Shallow donors Eg = 1. 59 e. V 1. 21 e. V 0. 9 e. V 0. 6 e. V Thermal transitions 1 e. V Optical transitions 1. 47 e. V Ge 2+/Ge 3+ (R-center) 0. 69 e. V Fe 2+/Fe 3+ (R-center) 0. 38 e. V 0. 12 e. V A center Freiburger Materialforschungszentrum FMF Valence band Phonons M. Fiederle