P09

Redshifted and Blueshifted Photoluminescence Spectra of InAs/InP Quantum Dots
upon Amorphization of Phase Change Material
Nurrul Syafawati Binti Humam, Yu Sato, Motoki Takahashi, Nobuhiro Tsumori, Toshiharu Saiki
Graduate School of Science and Technology, Keio University
nurrul@saiki.elec.keio.ac.jp
ABSTRACT
We have experimentally demonstrated a new method to control the emission energy of semiconductor quantum dots
(QDs), which is by applying strain using volume expansion of phase change material (GeSbTe) upon amorphization.
The emission energy of QDs was shifted to both higher and lower upon amorphization of phase change material. In
this study, we analysed the stress applied on QDs by developing a two-dimensional finite element model. Based on
the simulation result, the energy shift is negative at the shallow area beneath the flat part of indenter. On the contrary,
the energy shift is positive beneath the edge region of indenter. This result is further clarified by conducting aphotoluminescence (PL) spectroscopy of InAs/InP QD sample deposited by a layer of phase change material where
PL intensity mapping over amorphous region was performed. Our experimental results agree with the FEM simulation
result.
Keywords: Phase change material, volume expansion, quantum dot, energy shift

1. INTRODUCTION
Semiconductor quantum dots (QDs) have shown great promise as efficient single photon emitters and entangled
photon sources, making them attractive for quantum communication applications. One of the main challenges forrealizing applications is precise control of energy in QDs. The three main approaches to tune emission energy are
externally applied magnetic field, electric field and mechanical strain. The existing techniques have not shown precise
energy control of individual QDs. Therefore, we have experimentally demonstrated a new approach to precisely
control emission energy of QDs by applying a local strain on QDs using volume expansion upon amorphization ofphase change material [1]. In the past experiments, we observed both redshift and blueshift of PL peak energy of QDs
upon amorphization of phase change material. In this paper, we investigated the stress distribution and energy shift
distribution induced by the volume expansion of phase change material by employing finite element (FE) method.
2. SIMULATION
A two-dimensional FE model was developed to investigate the stress distribution in sample. Figure 1 illustrates thegeometry of the model. Simulation was simulated assuming the apex of the indenter (a-GST) applies compressive
stress on the top of InP surface. An InAs QD was placed 100nm below the surface of the sample along y-axis. Theindentation force was chosen to regenerate a 2meV redshift at 100nm beneath the top of InP surface. Energy shift wascalculated by employing equation (1), which provides the shift of QD emission energy induced by [001] compression
[2].
∆1

23σ

1σ(1)

Y and v are Young’s modulus and Poisson’s ratio respectively. σ andare mean stress components anddeviatoric stress components respectively. The first term in Equation (1) shows the energy shift due to hydrostaticstress, while the second term in Equation (1) corresponds to the energy shift due to uniaxial stress.

Figure 1 Geometry ofo model.

Figure 2 E
Energy shift distributiondinn simulation mmodel.

Figuure 2 presentss the energy shift distribuution in modeel obtained thhrough calcululation. In Fig
gure 2, one canbserve that thhe resultant compressivecstressson InP
P causes a reddshift of emisssion energy at the shallow
w area beneaathobthhe flat part off the indenterr, and a blueshift of emisssion energy beneathbthe edge
eregion oof indenter. ThisT simulatioon
reesult agrees w
well with ourr previous exp
perimental reesults which showsboth redshift and bllueshift upon amorphizatioonof phase changge material.

3. EXPERIMENTA PL spectroscopy of low
w density InA
As/InP QD ssample depoosited by a laayer of GeTe
Te film was performed.
pAAllmeasurements
ms were conduccted at low teemperature. TTo create an amorphousamark,ma nanoseecond Q-swittched laser wasw
foocused througgh a microscoope objectivee lense (N.A==0.65) at exciitation waveleength 532nm
m. PL spectra were measured
att every 200nnm step acrooss a 2μm×2μμm area. Duuring PL meaasurement, QDs
Q
were exxcited using He-NeHlaser atexxcitation wavvelength 6322.8nm. Shift ofo PL peak eenergy of QDDs before and after the foformation of the amorphousmarkmwere dettermined at 4 points. Pointt A and pointt C are at the edge of the amorphousammark, point B is at the centterof the amorphoous mark andd point D is at the crystalliine region.
Baseed on the exxperimental reesults, at poiint A and pooint C, a blueshift, 0.4meeV of PL peak energy wasw
obbserved. At ppoint B, the PL peak eneergy was reddshifted as laarge as 0.8meeV. PL peakk energy at point D did notnexxhibit energyy shift. Thesee results imply that the P
PL peak energ
gy of QD at the center oof the amorph
hous mark wasw
reedshifted, whhile the PL peeak energy off QDs at the eedge region bllueshifted.
4. CONCLU
USION
We have obtained eneergy shift disstribution in sample by developingda two-dimensiional finite element
emodeel.
Redshift
Rwas oobtained at thhe shallow area beneath thhe flat part off the indenter, and blueshiift was exhibiited at the edge
reegion of the iindenter. We have also ex
xperimentallyy demonstrateed the validity
y of this simuulation result by performinnga two-dimensiional PL intennsity mappinng over an ammorphous marrk, which shoows good agrreement with the simulatioon
reesult.
ACKNOWLAEDGEMEN
NTThisT
research is supportedd by a Grant--in-Aid for S
Scientific Ressearch (B) from the Miniistry of Educcation, Culturre,Sport, Sciencee, and Technoology of Japan. We wouldd like to thankk R. Kubota, P.
P Regreny annd M. Gendry for providinng
us QD sample, and K. Yusuu for depositiing GST filmm.
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