Arpan Deyasi 1 , N. R. Das 2
1 Dept of ECE, RCC Institute of Information Technology, Kolkata, INDIA-700015
2
Institute of Radio Physics & Electronics, University of Calcutta, INDIA-700009
1 deyasi_arpan@yahoo.co.in;
2 nrd@ieee.org
Abstract: Oscillator strength and absorption cross-section of core-shell triangular quantum wire is computed for intersubband optical transition between ground state and first excited state. Results show that both oscillator strength and peak magnitude of absorption cross-section decreases with increasing dimension, and the rate is significant when nonparabolic dispersion relation is taken into account. Findings are important for designing optical emitter/detector using core-shell triangular quantum wire.
Keywords Oscillator strength, absorption cross-section, intersubband transition, core-shell structure
1. Introduction
3. Results
Electronic and photonic properties of semiconductor quantum wire has attracted interest of researchers [1] due to the possibility of design novel devices [2]; performance of which precisely depends on its quantized energy states. Positions of energy levels are function of geometry of the wire [3] and of material composition [4]. Recently, core-shell structure becomes an important candidate due to the possibility of wider tuning range of emission/absorption spectra and higher absorption cross-section. In present paper, authors computed oscillator strength for core-shell triangular quantum wire for optical transition between ground and first excited states, and corresponding absorption crosssection is evaluated considering InAs/Ga
0.47
2. Mathematical Modeling
The efficiency of transition between i th and j th quantized states is determined by the parameter oscillator strength, given by
In
0.53
As as material composition. Dimensions are varied to observe the change of the parameters with wider range of incident radiation considering nonparabolic band structure, and peak of the cross-section is also measured.
Fig in left shows oscillator strength as a function of core width, and Fig in right shows absorption crosssection with incident energy. With increase of core dimension, oscillator strength monotonically decreases, whereas the rate is almost negligible when parabolic dispersion relation is considered.Simultaneously crosssection peak appears at lower magnitude of incident radiation. The shift of peak position is larger for parabolic band compared to the nonparabolic one.
Again, since the transition energy increases due to nonparabolicity, so the peak appears at lower magnitude of incident radiation. But the shift of transition energy is very small with change of layer thickness in either of the quantized direction, so the shift of cross-section is almost negligible for nonparabolic dispersion relation. f ji

2 m
* 
E j , i
 2 j z i
2
(1) whereΔE j,i
is the intersubband transition energy,
Absorption cross-section can be computed from the knowledge of oscillator strength as
 ji
 q
2
T
2

0 m
* nc f ji



1

T
2


E
 

E j , i


2




1
(2)
4. References
[1] Kim, D. H., et. al., “Electronic structures and carrier distributions of T-Shaped Al x
Ga
1-x
As/Al y
Ga
1-y
As quantum wires fabricated by a
Cleaved-Edge Overgrowth method”, Jour. Nanosc.Nanotech, 12,
5687-5690 (2012)
[2] Qian, F., et. al., “Core/Multishell nanowire heterostructures as multicolor, high-efficiency light-emitting diodes”, Nano Letters 5,
2287-2291 (2005)
[3] Khordad. R., “Quantum wire with parallelogram cross-section: optical properties”, Jour. Theo. App. Physics 6(19), 1-7 (2012)
[4] Wong, B. M., et. al., “Nanoscale effects on heterojunction electron gases in GaN/AlGaN core/shell nanowires”, Nano Letters 11, 3074-
3079 (2011)