# Presentation: 701971

## PL studies of CdTe crystals ion-implanted with Cl, Cu, or P

**Shine Liu, Levi Gorrell -- Univ. of Toledo (****presented by ADC****)**

- 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 **λ** and power density
- study T-dependence
- study power dependence

**objectives of this study:**

**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

## PL dependence on CdTe crystal quality

_**“**__**second quality” Nikko XTAL**_

_**“**__**first quality” Nikko XTAL**_

_**PL dependence on CdTe crystal quality**_

**Notes:**
2nd NM CdTe crystal was etched by 2% HNO3 for 10s

## 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%)

**Beer’s Law:**
*I = I**o** exp(- d/d**o**)*

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

- do = 0.09m at 488nm
-     = 0.347m at 752nm

## for moderate doses, damage is annealed out at 400 C for 30 min.

_**best annealing occurs @ 400**__**o**__**C**_

**CdTe:Te, 1.25x10****13****/cm****2**

_**Ion implantation damage in CdTe can be annealed out at 400 **__**o**__**C**_

## Cl implantation in 

_**2**__**nd**__** quality Nikko XTAL**_

**1mW 488nm**** excitation**

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

- CdTe:Cl, 3x1016 /cm3

- after annealing

- before annealing

- CdTe:Cl, 1x1017 /cm3

- after annealing

- before annealing

- after annealing

- before annealing

- CdTe:Cl, 1x1018 /cm3

## Density and Power Dependence for Cl-implanted CdTe

- CdTe:Cl, 3x1016 /cm3

- CdTe unimplanted (Nikko #2)

- CdTe:Cl, 1x1018 /cm3

_**Density and Power Dependence for Cl-implanted CdTe**_
_** **__**488nm**__**, 40 K**_

- CdTe:Cl, 1x1017 /cm3

## Temperature dependent PL

## Cu implantation in 1st quality Nikko XTAL

- 4mW

- 1mW x2.2

- 0.3mW x4

- 0.1mW x6.5

- 0.034mW x13

**0.3mW 488nm**** excitation**

**Donor-Acceptor Pair **
**Cu****Cd**** ******** D  **

- h = Eg – Ed – Ea + **e****2****/(4********o****R)**

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

- 5

## Power-dependence of P-implanted CdTe PL

**e-A transition;**
**P****Te**** at  E****VB****+70 meV**

## Power dependence of three PL features in P-implanted CdTe with different densities

## 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 Cu****Cd****-Cl****Te** ??
- A-center (VCd -ClTe) transition appears at ~1.45 eV
- P implantation identifies acceptor state at EVB + 0.070 eV
- 	(increases with implant dose)