Dynamics of the matrix in DMS Type-II
quantum dot
systems
Collin Brown1, Vincent R. Whiteside1, Ian R. Sellers1,
Athos Petrou2, W-C. Chou3
1 - University of Oklahoma
2 – University at Buffalo SUNY
3 – National Chiao Tung University
Work supported by NSF DMR-1305770
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
Schematic
ZnTe/(Zn,Mn)Se
ZnMnSe capping layer (10% Mn) (50 nm)
(Zn,Mn)Se
ZnTe
(Zn,Mn)Se
ZnTe QDs
ZnMnSe buffer layer (10% Mn)
ZnSe
ZnSe (MEE)
GaAs Substrate
CB
(50 nm)
(50 nm)
Type I
VB
(Zn,Mn)Te/ZnSe
ZnSe
ZnSe capping layer
ZnSe (MEE)
GaAs Substrate
(Zn,Mn)Te
(50 nm)
ZnMnTe QDs (5% Mn)
ZnSe buffer layer
Type II
CB
(50 nm)
VB
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
ZnSe
Photoluminescence at 4K
Barrier Peak
• B. Barman et al., Physical Review B 92, 035430 (2015).
• I. R. Sellers et al., Physical Review B 82, 195320 (2010).
• I. R. Sellers, V. R. Whiteside, A. O. Govorov, W. C. Fan, W. C. Chou, I. Khan, A.
Petrou, and B. D. McCombe, Physical Review B 77, 241302 (2008).
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
Temperature Dependence
• The barrier region in both samples exhibits
classic Varshni behavior due to temperature.
• Both samples also exhibit fast quenching of
the photoluminescence (PL) after 25K
ZnMnSe EA = 17 meV
ZnSe EA = 14 meV
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
Intensity vs Field
ZnTe
ZnMnSe
-1/2
+1/2
CB
𝜎−
𝜎+
σ+
σ-
VB
+3/2
-3/2
+1/2
CB
𝜎+
𝜎−
-1/2
+3/2
+1/2
VB
-1/2
-3/2
Polarization is calculated using Peak Height – 𝑃 =
𝜎+ −𝜎−
𝜎+ +𝜎−
× 100
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
Polarization
10% Mn
B. Barman et al., Physical Review B 92, 035430 (2015).
5% Mn
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
Temperature Dependent Polarization
ZnSe Matrix
ZnMnSe Matrix
The matrix exhibits classic
paramagnetism. We see
increasing polarization with
field, and decreasing polarization
with temperature.
The matrix exhibits no behavior,
which is normal considering
there is no Mn in this Matrix.
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
Zeeman Energy
Here is the Zeeman energy
behavior for a conventional
paramagnet.*
Here is what we see.
* J. K. Furdyna, Journal of Applied Physics 64, R29 (1988).
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
Zeeman Energy Behavior
σ+
σ-
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
Future Work
• Magnetoreflectivity - This will help us determine whether we
are really seeing σ• We will reverse the applied magnetic field to measure
hysteresis in the photoluminescence spectra.
• We are collaborating with the Colorado School of Mines to
understand exactly where the Mn impurities are in our samples.
– Cross Sectional Transmission Electron Microscopy (TEM)
– Atomic Force Topography (AFT)
• Questions?
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html