Room-Temperature Transport of Indirect Excitons in(Al,Ga)N/GaNQuantum Wells

Abstract

We report on the exciton propagation in polar (Al,Ga)N/GaN quantum wells over several micrometers and up to room temperature. The key ingredient to achieve this result is the crystalline quality of GaN quantum wells (QWs) grown on GaN template substrate. By comparing microphotoluminescence images of two identical QWs grown on sapphire and on GaN, we reveal the twofold role played by GaN substrate in the transport of excitons. First, the lower threading dislocation densities in such structures yield higher exciton radiative efficiency, thus limiting nonradiative losses of propagating excitons. Second, the absence of the dielectric mismatch between the substrate and the epilayer strongly limits the photon guiding effect in the plane of the structure, making exciton transport easier to distinguish from photon propagation. Our results pave the way towards room-temperature gate-controlled exciton transport in wide-bandgap polar heterostructures. PACS numbers:1 arXiv:1603.00191v1 [cond-mat.mes-hall]

Trapping Dipolar Exciton Fluids in GaN/(AlGa)N Nanostructures

“…E BS can be used for estimating the exciton density as n = E BS /φ 0 , where φ 0 = 1.5×10 −13 eV cm −2 is the coefficient extracted from the self-consistent solution of the Schrödinger and Poisson equations (see also Supporting information). 17,25,28 This estimate could be improved taking into account excitonic correlations (see discussion below). 22,33,34 Let us compare the spatial profiles of the emission from the bare QW and circular traps.…”

“…4 (c-d) are obtained in the rough semi-phenomenological approximation described above, neglecting excitonic correlations: n = E BS /φ 0 , where φ 0 is deduced from the self-consistent solution of the Schrödinger and Poisson equations. The same approximation was used in Refs., 17,28 and it is conceptually similar to the plate capacitor model. 38,39 The effect of the exciton-exciton interactions was investigated theoretically and experimentally in Refs.…”

“…These may include nonradiative losses, 23 megavolt per centimeter-strong built-in electric fields, 24 an exponential dependence of the lifetime on the exciton density under high excitation conditions, [25][26][27] and the guided-and-scattered light that must be distinguished from the exciton photoluminescence (PL). 17,28 In this letter we overcome those challenges and report on the realization of ∼ 10 µm ×50 µm-size thermalized exciton fluid, trapped in the plane of a GaN/(GaAl)N quantum well grown on a free-standing GaN substrate. Our objective is to obtain an area uniformly filled with excitons, with a density that can be controlled by the excitation power.…”

“…The emission from the bare surface ( These effects are due to the screening of the electric field along the growth direction induced by the photocreated carriers: the highest density under the pumping spot corresponds to the maximum screening (lowest electric field), and thus to the highest emission intensity and energy. 17,25,28 The pump-induced emission energy shift is referred to as the blue shift, E BS .…”

Indirect excitons in van der Waals heterostructures at room temperature

“…IXs were explored in various III-V and II-VI semiconductor QW heterostructures based on GaAs 2,3,[8][9][10][11][12][13][14] , AlAs 15,16 , InGaAs 17 , GaN [18][19][20] , and ZnO 21,22 . Among these materials, IXs are more robust in the ZnO structures where their binding energy is about Van der Waals structures composed of atomically thin layers of TMD offer an opportunity to realize artificial materials with designable properties, forming a new platform for studying basic phenomena and developing optoelectronic devices 4 .…”