Exploring Coulomb interaction in piezoelectric materials for assisting the laser cooling of solids

Abstract

Realization of anti-Stokes cooling requires high enough photon extraction efficiency as well as quantum efficiency, making the implementation of this technique extremely difficult for semiconductors. Here, for the first time, we demonstrate that the Coulomb interaction between photogenerated electron-hole pairs in strong piezoelectric materials such as GaN/InGaN quantum wells could assist laser cooling. By comparing to the cavity back-action mechanism, we also explain how this process depends upon laser detuning with respect to bandgap. To demonstrate the advantage of this method even further, we present simulations by using experimentally reported parameters of GaN and In 0.15 Ga 0.85 N, in order to conclude that the net cooling is indeed possible even with current III-nitride growth technology. 1-INTRODUCTIONAnti-Stokes phenomenon has been investigated extensively for achieving the laser cooling of solids [1][2][3][4]. This process is based on extraction of the phonon energy by means of photo luminance (PL). The photogenerated electron hole pairs gain energy from the phonon bath and consequently release the energy upon recombination. In this regard, if the radiative recombination dominates all the other processes and the emitted PL can get out of the medium (see Ref[5] as an example of increasing the extraction efficiency), then anti-Stokes laser cooling will be possible. The first laser cooling of a solid (ytterbium doped glass) was achieved in 1995 by Epstein et al [4]. However, for semiconductors, due to strict quantum efficiency requirements and lower extraction efficiencies, this goal couldn't be achieved until recently when Zhang et al [6] showed anti stokes refrigeration in CdS nano-belts. It should be noted that there have been numerous attempts to increase the quantum efficiency of III-V semiconductors. This trend also led to growth of semiconductors which can have potential use for laser cooling applications [7]. As for the case of enhancing the extraction efficiency, some novel techniques have been proposed such as attaching a dome lens to the semiconductor[7], using surface plasmon polaritons[8], Mie scattering [5],evanescent coupling through a nano-gap [3], and surface roughening [9].Another technique of laser cooling, known as optomechanical backaction, can be implemented when the optical and mechanical modes of a cavity are coupled effectively [10]. In this case, cooling -or amplification of the mechanical mode depends on laser detuning. Metzger et al [11] showed the utilization of this method for cooling a gold coated silicon membrane. The drawback of this method is the involvement of only one vibration mode of the cavity which reduces its effectiveness when dealing with a phonon bath in a solid.