PL studies of CdTe crystals ionimplanted with Cl, Cu, or P

1
PL studies of CdTe crystals ion-implanted with
Cl, Cu, or P
Shine Liu, Levi Gorrell -- Univ. of Toledo
(presented by ADC)
difficulties with PL studies

• PL intensities show everything and depend on
  everything!
• temperature, laser wavelength, laser power, other
  defects and impurities, grain boundaries
• upper and lower states
• difficult to quantify densities

objectives of this study

• study PL behavior in well-characterized, crystal
  CdTe with known densities of dopants (ion
  implanted)
• verify that implantation-induced damage can be
  annealed out
• determine best excitation ? and power density
• study T-dependence
• study power dependence

2
first quality Nikko XTAL
PL dependence on CdTe crystal quality
Keystone XTAL
second quality Nikko XTAL
3
SRIM (a Monte Carlo simulation program) Cl ion
implantation in CdTe

• multiple energies used to obtain uniform density
  of Cl in CdTe

400 keV
400 keV (72.5) 200 keV(18.8) 100 keV(8.7)

• vacancy density from collision events is very
  high (1900/ion)

Beers Law I Io exp(- d/do)
do 0.09?m at 488nm 0.347?m at 752nm
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Ion implantation damage in CdTe can be annealed
out at 400 oC
best annealing occurs _at_ 400oC
for moderate doses, damage is annealed out at 400
C for 30 min.
CdTeTe, 1.25x1013/cm2
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Cl implantation in 2nd quality Nikko XTAL
after annealing
CdTeCl, 3x1016 /cm3
before annealing
1mW 488nm excitation
after annealing
CdTeCl, 1x1017 /cm3

• (as-imp weak PL)
• after annealing several PL features increase
  with Cl density

before annealing
after annealing
before annealing
CdTeCl, 1x1018 /cm3
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Density and Power Dependence for Cl-implanted
CdTe 488nm, 40 K
CdTeCl, 1x1017 /cm3
CdTe unimplanted (Nikko 2)
CdTeCl, 1x1018 /cm3
CdTeCl, 3x1016 /cm3
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Temperature dependent PL
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Cu implantation in 1st quality Nikko XTAL
0.3mW 488nm excitation
Donor-Acceptor Pair CuCd ? D
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4mW
1mW x2.2
h? Eg Ed Ea e2/(4???oR)
0.3mW x4
0.1mW x6.5

• close D-A can increase with power because
  recombination is fast
• distant D-A, more numerous, but saturate with
  power because recombination is slow

0.034mW x13
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Power-dependence of P-implanted CdTe PL
e-A transition PTe at EVB70 meV
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Power dependence of three PL features in
P-implanted CdTe with different densities
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conclusions

• much cleaner PL spectra on crystals than on pc
  films
• ion implantation helps to quantify the impurity
  density
• Cl enhances several PL features
• is it just improving crystal quality?
• are these all Cl-related features?
• Cu-related D-A pair transition appears at 1.49
  eV
• is this CuCd-ClTe ??
• A-center (VCd -ClTe) transition appears at 1.45
  eV
• P implantation identifies acceptor state at EVB
  0.070 eV
• (increases with implant dose)