Exciton to two-dimensional electron-hole photoluminescence transitions driven by the quantum Hall effect in photoexcited heterojunctions

Abstract

A comprehensive experimental study of the photoluminescence (PL) spectral evolution under a magnetic field (B ^ 25 T) applied perpendicularly to a high-mobility two-dimensional electron gas (2DEG), is performed on modulation-doped GaAs/AlGaAs heterojunctions at TL=0.3 K. The abrupt transfer of the free exciton to hole-2DEG PL occurring at integer and fractional filling factors is analyzed in a phenomenological model, wherein free excitons photogenerated in the GaAs layer dissociate into a 2D electron and 3D hole near the 2D-electron channel. Such magnetic field induced exciton-(2De-h) transitions are able to explain the remark able strong PL anomalies in single hetrojunctions as compared to those observed in modulation-doped quantum wells.

Circular polarization in n-type resonant tunneling diodes with Si delta-doping in the quantum well

“…This band presents a strong red shift and a decreasing intensity with increasing voltages [12][13][14][15][16][17][18][19][20][21]. This voltage dependence is consistent with an emission involving a 2DHG gas under applied voltage and light excitation.…”

Microwave-modulated photoluminescence of a two-dimensional electron gas

“…It is worth noting that similar PL spectral shifts were previously observed when n 2D was varied by optical depletion, and the different response of the excitonic and 2DEG PL to the n 2D variation was explained by the appearance of 2DEG puddles in photoexcited MDQWs. 5 This difference in the MPL spectra for both transitions is clearly observed in the single heterojunction. Its spectrum consists of a low-energy PL band due to the 2DEG which occupies the lowest Landau level and of high-energy PL lines due to bulk excitons in the GaAs buffer layer.…”

“…Figure 7͑b͒ displays the PL and MPL spectra for the low-density 33-nm-wide MDQW ͑n 2D = 2.5ϫ 10 10 cm −2 ͒ where excitonlike ͑charged and neutral excitons X t − and X 0 ͒ and 2DEG PL bands coexist at B Ќ Ͼ 3.5 T ͑ Ͻ 0.5͒. [3][4][5] The MPL spectrum shows that the 2DEG ͑and H͒ PL bands are affected differently by mw irradiation as compared to the X t − and X 0 bands. The former show a shift while the charged ͑and neutral͒ exciton PL lines exhibit only a decreased PL intensity ͑ϳ10% ͒ under mw irradiation.…”

“…1 For electron filling factor =2L B 2 n 2D Ͻ 1 ͑n 2D is the 2DEG density, L B the magnetic length͒ additional, high-energy bands appear in the PL spectrum of MDQW's, 2 and these were recently intensively studied. [3][4][5] The effectiveness of PL spectroscopy is further enhanced by modulating it by microwave ͑mw͒ irradiation. The basic process of mw-induced PL changes in semiconductors is electron heating due to mw absorption by free electrons, 6 so that the electron temperature T e exceeds the lattice temperature T L .…”

Softening of the tunneling gap in modulation-doped GaAs/AlGaAs asymmetric coupled double quantum wells in magnetic fields

“…As a consequence, formation of low lying excitations such as excitonic complexes, Skyrmion, and spin wave transitions have been reported by a number of groups. [1][2][3][4][5][6][7][8][9] The changeover from free carrier to neutral ͑X 0 ͒ and to charged ͑X − ͒ exciton transitions play an important role in the understanding of electron-hole ͑e-h͒ correlations. Rashiba et al 10 claimed that such a changeover occurs as a consequence of hidden symmetry that is inherent in the case of 2DEG in a symmetric square quantum well without invoking Landau level mixing.…”