Nanooptics and photonics

Islands of electron-hole liquid
in 2D heterostructures
Chernyuk A.A., Sugakov V.I
Theoretical Physics Department, Institute for Nuclear Research, NAS of Ukraine
prosp. Nauki, 47, Kyiv 03680, Ukraine, inr@ukr.net

The formation of the electron-hole liquid (EHL) at intensive laser irradiation of semiconductors has been intensively investigated in materials (see [1]). The phenomenon is observed as the emergence of EHL droplets among the exciton gas, which is excited by light. A promising perspective is the detection of EHL in a two-dimensional (2D) system, in which the interaction between charges is more intense than in bulk material.
In recent years, the phase transition of «the exciton gas – EHL» has been observed in semiconductor Si/SiGe/Si heterostructures [2] and in silicon layers, limited by high SiO2 barriers on both sides [3], in InGaAs/GaAs/InGaAs double quantum wells [4]. In the region of coexistence of the phases in 2D system, EHL must form in the shape of islands. The theory of formation of islands of EHL in 2D semiconductor heterostructure is studied in this paper. In the calculations, a statistical model was used to study the islands of the condensed phase of excitons in quantum wells of semiconductors [5]. The interaction between the islands is mediated through the diffusion fields of the excitons: the capture of excitons by a certain island affects the density of excitons near adjacent islands and consequently their growth. Due to the finite lifetime of excitons and the processes of recombination of electrons and holes in the islands, the stationary structure can exist only in the presence of pumping, which creates the excitons.
We considered, that excitons are created by the light in  the restricted regions of the quantum well. Afterwards the EHL islands are formed on these regions, are created by lighting on a plane of the quantum well. The formation of islands of EHL have been studied in the following types of the exciton generation regions.
1. A semiconductor quantum well, in which the exciton generation region has the form of a narrow strip, and the islands can be situated in the direction of the strip only. It was obtained that the islands are formed at the pumping rate, which is higher than some threshold value. The value of radius of islands grows with increasing pumping, and the distance between islands shortens.
2. The irradiation area has a shape of a disk. The number, distribution and mutual situation of the islands varies depending on the intensity of the irradiation and the radius of the disk. The island can be located in the center of the irradiation area. The islands can be located near the perimeter of the circle, or in the center and near the perimeter. Also EHL can be located along a ring near the perimeter. As the radius of the disk grows, the number of islands near the perimeter increases.

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