Superimposed Quantum Dots: Emerging Optoelectronics

Perspective

Ann Materials Sci Eng. 2021; 5(1): 1040.

# Superimposed Quantum Dots: Emerging Optoelectronics

Rostami A1,2*

¹Photonics and Nanocrystal Research Lab (PNRL), Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz, Iran

²SP-EPT Lab, ASEPE Company, Industrial Park of Advanced Technologies, Tabriz, Iran

*Corresponding author: Ali Rostami, Photonics and Nanocrystal Research Lab (PNRL), Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz, 5166614761, Iran; SP-EPT Lab, ASEPE Company, Industrial Park of Advanced Technologies, Tabriz, 5364196795, Iran

Received: August 02, 2021; Accepted: August 18, 2021; Published: August 25, 2021

## Perspective

As everybody knows that electron, phonon, and photon transport in solids (crystals) depends on lattice physical properties. Manipulation of propagation properties needs to manipulate crystal parameters such as lattice constant, atoms in the lattice, etc. There are a limited number of crystalline structures in nature to manipulate charge, phonon, and photon transfer in electronics, acoustics, and photonics. The basic problem is how one can make single crystals with desired charge, phonon, and photon transfer performance? Also, how one can manipulate the mechanical, optical, and electrical performance of a device? It seems that nanotechnology and especially nanoparticles and superimposed nanocrystals can help to solve this problem. In this short letter, the superposition of Quantum Dots as a solution to enhance the capability of device designers in this regard is presented, discussed, and demonstrated by simple numerical simulation. If we use the superimposition of QDs, we can realize multi wavelength lasers in a single cavity [1,2]. The ultra-broadband semiconductor optical amplifiers can be implemented by this idea [3]. Multi wavelength photodetector with multi-electrical output is another most important application that can be realized using this idea [4]. High-efficiency solar concentrator based on superimposed QDs is introduced in [5]. Other interesting applications can be realized using the proposed idea too. All these advantages are related to optical and electrical properties dependency on the size of nanocrystals [6]. So, it is possible to make different crystals using the superimposition of well-known crystals. To demonstrate that, first, by choosing different crystals, and using the superposition of those, it is shown that the obtained structure is similar to a new crystal with a lattice constant that depends on initial superimposed crystal lattice constants as well as a geometrical combination of those. In the second part, we show that using colloidal QDs, it is so easy to combine different QDs with different sizes in a unique solution and a superimposed QDs with the desired density of each QDs will be available.

Theoretical Analysis- To easily modeling the concept, we assume that a periodic signal shows periodic potential (crystal potential) for real crystals. Then, based on normal methods in solid-state physics, it is so easy to model superimposed QDs. In this case, different gated periodic structures are superposed to make the superimposition of QDs. Finally, using simple mathematical calculation, we show that conclusion of the superimposed QDs is similar to a new periodic structure. On the other hand, using the superimposed QDs with specific distributions, a new single crystal can be achieved. Then electrical, acoustical, and optical properties will be superimposed of basic crystals.

$\boldsymbol{\mathit{V_{m}(\mathit{r})=}\sum_{n=0}^{\infty&space;}a_{m_{n}}cos(nK_{m}r)}&space;1$

where Vm, m, amn, Km and r are the potential energy of the crystal, index of QDs, expansion coefficient, lattice vector, and position respectively. In this relation, we assumed that the array of QDs can be approximated by cosine Fourier series expansion and so the first term is enough to approximate that. Using this approximation in the following superposition of M type array of QDs can be expressed as follows.

$\boldsymbol{\mathit{V_{total}(\mathit{r})=}\sum_{j=0}^{m}a_{1_{j}}cos(K_{1_{j}}r)}&space;2$

where Vtotal, j, a1j, K1j, M, and the r are the superimposed potential energy of the whole crystal, index of lattice, first term of expansion coefficient, lattice vector, number of superimposed QDs, and position respectively. As an example using two types of similar QDs (a little bit different from mole fraction point of view), it is possible to obtain a crystal with a lattice constant that is an average value of two lattices made by QDs. Also, using selective energy contacts, one can access each lattice separately without perturbing others. As it was shown [1,2] using the proposed idea two-wavelength laser using a single cavity is available and this is a new way to integrate optical systems (Figure 1). It should mention that using selective energy contacts, one can populate only one of QDs and so a single wavelength lasing. If two contacts are used, the two groups of QDs can be populated and simultaneously two-wavelength oscillations will have appeared. It can be generalized to have multi wavelength lasing. Also, this idea can be used to fabricate high-efficiency LEDs and white LEDs.