Donor Impurities as a Probe of Electron Correlations in a Two-Dimensional Electron Gas in High Magnetic Fields

Abstract

Many-electron effects have been observed in far-infrared magnetospectroscopic studies of GaAs͞ AlGaAs multiple quantum wells (QWs), d doped with Si donors in both well and barrier centers. With increasing excess electron densities in the QWs the negative donor ion ͑D 2 ͒ singlet and triplet transitions are substantially blueshifted, exhibiting cusps at integer and fractional filling factors. At high magnetic fields the many-electron system appears to approach a collection of isolated twoelectron D 2 ions. Exact diagonalization studies of donor and confined electrons show the importance of electron correlations and localization at high magnetic fields in understanding this behavior.

High-Pressure Studies of Semiconductors in the Far-Infrared: Donor States in Quasi-2D

“…(See, for example, Refs. [15][16][17][18] and citations therein.) Here, we shall illustrate the potential of FIR-DAC experiments by discussing our latest results on cyclotron resonance (CR), neutral donors (D0), and negatively charged donors (D-) in modulation-doped GaAs/AlGaAs MQWs.…”

“…The progression with increasing total electron density (labels to the right) clearly shows how the D0 1s → 2p+ transition becomes dominated by the D -singlet line when more than one electron per QW-donor is available. When more than two electrons per QW-donor is available, the D-singlet line undergoes a blue shift that arises from many-electron effects [17] . The character of this transition then changes from that of an isolated D-ion to that of a donor-bound magnetoplasmon.…”

“…8a) the spectra for this sample are characterized by a strong CR line, and a weaker absorption feature at higher energy. The latter is identified as the D-singlet-like transition, based on its blue-shifted energy position relative to the analogous singlet transition for an isolated D-ion [17], given by Eq. (1).…”

Interacting Electrons and Holes in Quasi-2D Quantum Dots in Strong Magnetic Fields

“…This belief was somehow mitigated by the discovery of bound (403) "charged excitons" in strong magnetic fields [3], and the development of the understanding of these charged excitons in emission from the 2DEG [4][5][6][7]. To gain access to optically detected properties of the electronic system, the breaking of hidden symmetries was introduced by increasing the separation of holes and electrons [8], by localizing holes on acceptors [9], by introducing impurities into the electron gas [10], and by laterally confining the electron gas into quantum dots [11]. Recent experiments [12][13][14] show that it is now possible to fabricate high quality self-assembled quantum dots confining both electrons and holes and to study their optical properties in a strong magnetic field [14], i.e.…”

Photoluminescence from fractional quantum Hall systems: Role of separation between electron and hole layers

“…The optical properties of quasi-two-dimensional (2D) electron systems in high magnetic fields have been extensively studied in the recent years both experimentally [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and theoretically. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] In symmetrically doped quantum wells (QW), where both conduction electrons and valence holes are confined in the same 2D layer, the photoluminescence (PL) spectrum of an electron gas (2DEG) probes the binding energy and optical properties of neutral and charged excitons (bound states of one or two electrons and a hole, X = e-h and X − = 2e-h), rather than the original correlations of the 2DEG itself.…”