Dissociation of indirect excitons: Discontinuity and bistability in the tunnel current of single-barrier heterostructures

Abstract

We observed a new discontinuity and bistability in the tunnel current of a 12-nm single-barrier GaAs/AlAs p-i-n heterostructure where a system of spatially separated two-dimensional electron and hole (e-h) layers of equal and tunable density is realized. Both features appear at TՇ300 mK and are substantially enhanced in a magnetic field Bտ10 T perpendicular to the layers. They correspond to a discontinuity in the e-h density and in the phase of the current magneto-oscillations, which we suggest to arise from a transition between indirect excitons and the uncoupled e-h gases. ͓S0163-1829͑99͒12343-9͔

Bistability and discontinuity in the tunnel current of two-dimensional electron-hole layers

“…6͒; moreover, they allow an accurate determination of the HCS density at the transition. The values of the density obtained in this way naturally extend the ones deduced from the analysis of the full 1/B periodicity at Tϭ1.2 K, 1 as shown in Fig. 7͑a͒.…”

“…2͑b͒. 1,2 We denote the states corresponding to the upper and lower branch of the bistability the ''high-current state'' ͑HCS͒ and ''low-current state'' ͑LCS͒, respectively.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In these systems, the e-h recombination time can be made as long as 1 sec, therefore allowing thermalization of the carriers to the lattice temperature, a situation that is never reached in strictly 2D e-h systems because of the higher recombination rate. With respect to real atoms, 21 indirect excitons are particularly attractive because of their light mass, which is expected to allow condensation at T ϳ1 K, rather than in the K regime.…”

“…To date, most of the experimental work has been done on the optical properties of undoped double quantum wells ͑DQW's͒, [4][5][6][14][15][16] which provide a natural tool for obtaining charge separation. As already realized by Kuramoto and Horie, 17 another attractive possibility is to study the transport 1,2,20 and optical 3 properties of p-i-n single-barrier heterostructures ͑SBH's͒, in which 2D e-h layers of equal density accumulate under forward bias at opposite sides of the barrier. With respect to DQW's, p-i-n SBH's have several advantages.…”

“…1͒. [1][2][3] In such a device, two limits are known. At low densities (nϳ10 10 cm Ϫ2 ), Neves et al 20 have observed resonant tunneling via indirect exciton states, which manifests itself as peaks in the low-temperature (TՇ10 K) I(V) curves.…”