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S2211-3797(18)32638-X https://doi.org/10.1016/j.rinp.2019.01.039 RINP 2005

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Results in Physics

Received Date: Revised Date: Accepted Date:

22 October 2018 15 December 2018 13 January 2019

Please cite this article as: Al-Nashy, B., Al-Shatravi, A.G., Abdullah, M., Al-Khursan, A.H., InTlSb quantum dot structures, Results in Physics (2019), doi: https://doi.org/10.1016/j.rinp.2019.01.039

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InTlSb quantum dot structures B. Al-Nashy(1), Ali Gehad Al-Shatravi(2), M. Abdullah(3), and Amin Habbeb AlKhursan(3),* (1)

Science College, Misan University, Misan, Iraq.

(2)

Physics Deptartment, Science College, Thi-Qar University, Nassiriya, Iraq.

(3)

Nassiriya Nanotechnology Research Laboratory (NNRL), Science College, ThiQar University, Nassiriya, Iraq. * Corresponding author; e-mail: [email protected]

Abstract In this work, total (linear and nonlinear) optical absorption from InTl1-xSbx QD structures was studied. It is shown that these Tl-based QD structures have high absorption at long wavelengths. Nonlinear absorption at high power levels was preferred at some slow-light applications. The structures studied assess the possibility of infrared applications of Tl-based structures. Keywords: Quantum dot devices, Semiconductors, linear absorption.

1.

Introduction While the industry of long wavelength infrared photodetectors

depends on II-VI HgCdTe detectors, there is an insight to replace it by III-V semiconductors [1, 2]. This is related to the possible advantages of III-V semiconductors that depends on their property of strong covalent bonding, thermal stability, mechanical strength, and doping control [3]. 1

To do this important task, III-Sb based devices with low bandgap shown to be the milestone in these applications. They offer many possibilities like low electron effective mass and high mobility at room temperature, which is not found with HgCdTe devices [4]. The spectral range of III-Sb devices can be extended by adding a heavier elements such as Bi and Tl. Alloying Bi suffer from sever growth problems. InBi is a tetragonal structure, this reduces concentrations during it the equilibrium alloy is miscible [5, 6]. InTl1-xSbx has been considered as a candidate for infrared works due to many advantages. First, like HgTe, TlSb should be a semimetal, so the band gap of InTlSb should be capable of to cover the overall infrared wavelength spectrum by adjusting the thallium mole fraction. Second, in the contrary of InAsSb which is suffer from the lack of a lattice-matched substrate, TlSb should be lattice matched to InSb within 2%, thus offering the potential to realize good-quality device structures [3]. Quantum dot (QD) nanostructures gets important attention due to its superior characteristics originated from their atomic-like energy subbands which are size dependent. Since the fundamental importance of infrared devices in military and civil applications [1, 7], it is important to examine the structures that can work in this region. This work examines the total (linear and nonlinear) absorption from InTl1-xSbx QD structures.

2

It studies both linear and nonlinear contributions. The structure studied assess the possibility of Tl-based QDs for infrared applications.

2. Theory The linear and nonlinear optical absorption can be derived using the equation of motion of the density matrix with the perturbation approach of the density matrix elements. The total (linear and nonlinear) absorption is be expressed as follows [8],

h (1) h 3 (3) h Es

2

(1)

3 1 where h is the linear gain, h is the third-order nonlinear

absorption which results from suppression due to the beating between the resonant mode and the oscillation of another mode (s). Es is the optical electric field of mode s. The term 3 is related to the optical confinement factors. In the case of self-organized dots, an inhomogeneous broadening function D (E ) for the optical transition energy E is used in the density of QD states, in addition to the Lorentzian lineshape function

L E , h , to describe QD gain. Then, the optical linear absorption per QD layer of a self-assembled QD is expressed as [8]

3

(h) C0 (1)

dE M env

2

2 eˆ.Pcv D( E ) L( E , h)

i

[ fv ( E, Fv ) fc ( E , Fc )]

(2)

where the summation over i is carried out to account for all radiative transitions. The term M env

2

is the envelope function between the QD

electron and hole states which is considered as nearly unity. The term 2

eˆ.Pcv

is the momentum matrix of QD depending on the polarization of

light under the parabolic band model. eˆ is a unit vector in the polarization direction. Note that C0 terms

nb

, c , o , ,

mo ,

e2 with usual meaning of its scripts. The nb c 0 m0

' and E , are the background refractive index of the

material, the speed of light in free space, the permittivity of free space, the angular optical frequency, the free electron mass, and the optical transition energy, respectively [9]. The third-order nonlinear optical absorption per QD layer is expressed as [10]

(3)

(h) C0

dE M env

2

2 eˆ.Pcv D( E ) L( E , h)

i

[ fv ( E, Fc ) fc ( E, Fv )] ( E) ps where

4

(3)

2 3 6 e2 1 1 ( E ) e . pcv ( ) 5 m0 ns c wd h cc h vv

V 2 ) (1 ,s ) (1 h cv ( cc vv ) ( ) 1 V 2 V 2 ( E hs )2 (h cv ) 2 (1 2 ) (1 2 ( cc ) ( vv )

(4)

The term s is the injected optical signal angular frequency. The factor (1 , s ) is used to exclude the coherent spectral hole burning when

s and the detuning ∆ is defined as s . The terms h cc h / c , h vv h / v , and h cv h / in are determined by scattering events of carriers such as electron-phonon and electron-electron scattering. Here

c

and v are the relaxation time constants of electron

and hole distribution and

in

is the polarization relaxation time related to

the homogeneous broadening. The homogeneous linewidth is h cv . The value of 3 is about 0.7 where the Gaussian distribution was used to approximate the transverse field distribution [11, 12]. The relation 2

between the squared-amplitude of the electric field E s and the optical power ps is given by [8]

Es 2

ps 2ns c 0 wd

(5)

where w and d are the width and thickness of the active region of a QDSOA, respectively.

5

3. Results and discussion The structure InTl1-xSbx/InSb/GaAs was used to study the modal absorption in Tl-based QD structures at three mole fractions, they are: InTl0.08Sb0.92, InTl0.04Sb0.96, InTl0.02Sb0.98. This is a systematic study to specify the possible spectral ranges in the Tl-based QD structures and examine its infrared applications possibilities. The input signal power is used as a parameter to the QD-SOA. When Ps=0, then gain relation returns to the linear one. Other values of Ps for the nonlinear behavior. Fig. 1 shows the model absorption for InTl1-xSbx/InSb/GaAs QD structure for three Tl mole-fractions: 0.02, 0.04, and 0.08. Each curve has two peaks depending on the transition considered (ground- and excitedstate, GS and ES, transitions). The absorption peak was increased and shifted to longer wavelength with decreasing Tl-mole fraction in the dot. This is due to the bandgap decrease at low Tl mole fraction. This is with the conclusion in [13] where the radius of Tl atoms is similar to that of indium and the predominant cation in InTlSb is lighter and strengthening indium. Note that InSb is one of the smallest bandgap semiconductors at lowest mole fraction [8, 14]. Fig. 2 shows the effect of applying an input power of 20mW. A nonlinear behavior appears at the peak of GS transitions as a spectral hole. The peak increases at small mole fractions. The reason of this is

6

that QDs with small Tl mole fraction have low bandgap than that with high Tl mole fraction. This increases carrier relaxation in the QDs with small Tl mole fraction. Fig. 3 shows the nonlinear absorption under the power applied. While absorption was decreased with power, the spectral hole was increased with it. This suggests the choose of the required power for the demand application. For slow light applications, deep and wider spectral hole was required [15]. From Fig. 3, the 30mW was preferred than others. The figure shows many peaks in the absorption spectrum of the structures. While the ES peak was the highest one, other peaks (3rd and 4th) were reduced. Fig. 4 shows an increment of absorption with p-doping by ~1.5 times when QDs were doped by 3 1011 cm2 . It is well known that pdoping provides an extra concentration of holes to cover those holes thermalized between closely spaced states in QD [9, 10, 11]. This was resulted in increasing absorption.

4. Conclusions Total optical absorption, including both linear and third-order parts, for InTl1-xSbx QD structures was studied. High absorption was obtained. Nonlinear absorption at high power levels was preferred for 7

slow-light applications. The structures studied assess the possibility of infrared applications of Tl-based structures.

5. References [1] Sana N. Dwara and Amin H. Al-Khursan, "Quantum Efficiency of InSbBi Quantum Dot photodetector", Applied Optics 54, 9722-9727 (2015). [2] Sana N. Dwara and Amin H. Al-Khursan, “Two-Window InSbBi Quantum Dot photodetector”, Applied Optics 55, 5591-5595 (2016). [3] P. T. Staveteig, Y. H. Choi, G. Labeyrie, E. Bigan, and M. Razeghi, “Photoconductance measurements on InTISb/lnSb/GaAs grown by lowpressure metalorganic chemical vapor deposition”, Appl. Phys. Lett. 64, 460-462 (1994). [4] B. Al-Nashy and Amin H. Al-Khursan, “The Composition Effect on the Dynamics of Electrons in Sb-Based QD-SOAs”, Ch.8 pp.153-176, “Ch. 8” in "Selected Topics on Optical Amplifiers in Present Scenario”, S. K. Garai Ed., PP.153-176, ISBN 979-953-307-306-3, InTech, March 2012. [5] S. Iyer, S. Chowdhury-Nagle, J. Li, and K.K. Bajaj, “Theoretical study of InAsSb/InT1Sb superlattice for the far infrared detector”, Mat. Res. Soc. Symp. Proc. Vol. 421 (1996) Materials Research Society. [6] Mark van Schilfgaarde, Arden Sher, and An-Ban Chen, “InTlSb: An infrared detector material?”, Appl. Phys. Lett. 62, 1857 (1993). [7] Tahseen Dakhil, Samir M. Abdulalmuhsin, and Amin Habbeb ALKhursan, “Quantum efficiency of CdS quantum dot photodetectors”, Micro & Nano Letters. Accepted. DOI: 10.1049/mnl.2017.0777. [8] B. Al-Nashy and Amin H. Al-Khursan. “Linear and Nonlinear Gain of Sb-based Quantum-Dot Semiconductor Optical Amplifiers”, Recent Patents on Electrical Engineering 3, 232-240 (2010).

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[9] J. Kim, S. L. Chuang, “Theoretical and experimental study of optical gain, refractive index change, and linewidth enhancement factor of pdoped quantum-dot laser”, IEEE J Quantum Electron 42, 942-951 (2006). [10] H. Al-Husseini, Amin H. Al-Khursan, S. Al-Dabagh, “III-nitride QD lasers”, Open Nanosci. J. 3, 1-11 (2009). [11] J. Kim, M. Laemmlin, C. Meuer, D. Bimberg, and G. Eisenstein, "Static Gain Saturation Model of Quantum-Dot Semiconductor Optical Amplifiers" IEEE J. Quantum Electronics 44, 658-666 (2008). [12] B. Al-Nashy and Amin H. Al-Khursan, “Completely Inhomogeneous Density-Matrix Theory for Quantum-Dots”, Optical and Quantum Electronics 41, 989-995 (2010). [13] Todd Steiner Ed., Semiconductor Nanostructures for Optoelectronic Applications, Artech House, 2004. [14] M. Schilfgaarde, A. Sher, and A. Chen, “InTlSb: An infrared detector material?”, Applied Physics Letters 62, 1857 (1993). [15] B. Al-Nashy, S. M. M. Amin and Amin H. Al-Khursan, "Kerr effect in Y- configuration double quantum dot System", JOSA B 31, 1991-1996 (2014).

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Figures

Fig. 1: Total absorption for InTlSb QD structure.

10

Fig. 2: Effect of signal power on three mole fractions of the total absorption for InTlSb QD structure.

11

Fig. 3: Effect of signal power on the total absorption for In0.98Tl0.02Sb QD structure.

12

Fig. 4: Effect of doping on the total absorption for In0.98Tl0.02Sb QD structure. Linear absorption (red line) was set for comparison.

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