Synthesis and Spectroscopic Characterization of TM Doped II-VI Materials

Synthesis and Synthesis and Spectroscopic Spectroscopic

Characterization of TM Characterization of TM Doped II-VI MaterialsDoped II-VI Materials

Justin Allman, Andrew Gallian, John Justin Allman, Andrew Gallian, John Kernal, Sergey B. Mirov, Ph.D.Kernal, Sergey B. Mirov, Ph.D.

University of Alabama at BirminghamUniversity of Alabama at Birmingham

MotivationMotivation

Transition metal (CrTransition metal (Cr2+2+, Fe, Fe2+2+) doped II-VI (II-Zn; VI-S, ) doped II-VI (II-Zn; VI-S, Se) semiconductors are effective media for broadly Se) semiconductors are effective media for broadly tunable, mid-IR laserstunable, mid-IR lasers

Promise under optical, and possibly direct electrical Promise under optical, and possibly direct electrical excitationexcitation

Timely, predictable method for preparation of bulk Timely, predictable method for preparation of bulk crystals is neededcrystals is needed

Thin film, quantum well,Thin film, quantum well, and and quantum dotquantum dot structures structures should provide increased efficiency in energy should provide increased efficiency in energy migration from host crystal to TM dopant ionsmigration from host crystal to TM dopant ions

Two ExperimentsTwo Experiments

Synthesis of bulk Fe:ZnS crystals by Synthesis of bulk Fe:ZnS crystals by electrolytic colorationelectrolytic coloration

Comparison of fluorescence properties of Comparison of fluorescence properties of Cr:ZnSe bulk and thin film materialsCr:ZnSe bulk and thin film materials

One:One:Electrolytic ColorationElectrolytic Coloration

Electrolytic ColorationElectrolytic Coloration

past samples prepared from melt, vapor-past samples prepared from melt, vapor-growth techniques, or post-growth thermal growth techniques, or post-growth thermal diffusiondiffusion

each method has disadvantageseach method has disadvantages Electrolytic ColorationElectrolytic Coloration increases uniformity of increases uniformity of

concentration and decreases annealing timeconcentration and decreases annealing time

Background

Electrolytic Coloration (cont.)Electrolytic Coloration (cont.)Experiment: setup

3 kV

to ground

high voltage power supply

tungsten needle electrode

ZnS crystal

high voltage electrode plate iron (Fe) foil

thermal couple

ceramic insulator

spring adjustment system

Electrolytic Coloration (cont.)Electrolytic Coloration (cont.)

vacuum pressures (~10vacuum pressures (~10-5-5 torr) torr)

heated to 500-650°C continuously under heated to 500-650°C continuously under voltage (3.0 kV)voltage (3.0 kV)

annealed for 30 minutes to one hourannealed for 30 minutes to one hour

Experiment: procedure

Electrolytic Coloration (cont.)Electrolytic Coloration (cont.)

Transmission spectra:Transmission spectra:

(A) taken from two (A) taken from two different places on different places on Fe:ZnS prepared by Fe:ZnS prepared by electrolytic colorationelectrolytic coloration

(B) thermo-diffusion (B) thermo-diffusion doped Fe:ZnSedoped Fe:ZnSe

Results

Two:Two:Bulk vs. Thin Film FluorescenceBulk vs. Thin Film Fluorescence

Bulk vs. Thin FilmBulk vs. Thin Film

Thin films, because of smaller dimensions, Thin films, because of smaller dimensions, should exhibit increased efficiency of energy should exhibit increased efficiency of energy migration to TM dopant ions.migration to TM dopant ions.

Therefore, thin films are a better candidate for Therefore, thin films are a better candidate for fluorescence under electrical excitation.fluorescence under electrical excitation.

Background

Bulk vs. Thin Film (cont.)Bulk vs. Thin Film (cont.)Experiment: setup

Spectrograph

PbS detector chopper (800 Hz)

cylindrical lens (f = 15cm)

lens (f = 5cm)

GaAs substrate

beam

brewster angle (68°) Cr:ZnSe film (thickness 1 µm)

Ge filter

Bulk vs. Thin Film (cont.)Bulk vs. Thin Film (cont.)

cw Er-fiber laser modulated cw Er-fiber laser modulated at 800 Hz used as pump at 800 Hz used as pump beambeam

thin film spectra taken at thin film spectra taken at two different geometries: at two different geometries: at zero degrees and normal to zero degrees and normal to the monochromator slitsthe monochromator slits

Experiment: procedure

Bulk vs. Thin Film (cont.)Bulk vs. Thin Film (cont.)Experiment: procedure (cont.)

DETECTOR DETECTOR

normal geometry zero degree geometry

Bulk vs. Thin Film (cont.)Bulk vs. Thin Film (cont.)Results

Fluorescence spectra of (A) normal geometry thin film, (B) zero degree geometry thin film, (C) bulk sample

(At Right)Top: Output intensity at 2000 nm as function of pump powerBottom: (A) Transmission of thin film (B) difference in fluorescence spectra of zero degree and normal geometry thin film

ConclusionsConclusions

Evidence of diffusion by electrolytic coloration was obtained for Fe doped ZnS in a period of 30 minutes.

Differences in the fluorescence spectra of bulk and normal geometry thin film Cr:ZnSe as well as zero degree and normal geometry thin films were detected and explained due to cavity effect.

Conclusions (cont.)Conclusions (cont.)

Similarities in the fluorescence spectra of bulk and zero degree geometry thin film were explained by the fact that spontaneous photons of thin film imaged on the slit are not perturbed by the cavity.

Enhancement of thin film fluorescence at wavelengths matching cavity resonances was observed.

It was demonstrated that the stimulated processes are not responsible for enhancement of thin film fluorescence.

Questions?Questions?