New Photoluminescence Transition in GaAs InvolvingD−States

Abstract

Low temperature photoluminescence results from high purity epitaxial GaAs are presented, and a new type of transition involving negatively charged donor ions and neutral acceptors is identified. At low temperatures and excitation densities this becomes the dominant radiative process, with a linewidth of only ϳ1 cm 21 . The temperature dependence of this new transition reveals a binding energy of 2.65 6 0.35 cm 21 , consistent with the spectroscopic value of 2.8 6 0.2 cm 21 and with theoretical predictions. This is to our knowledge the first experimental determination of the D 2 binding energy in unperturbed GaAs. [S0031-9007(98)05493-3] PACS numbers: 78.55. -m, 71.55. -i D 2 states in single-valley semiconductors, formed when a shallow neutral hydrogenic donor ͑D 0 ͒ binds a second electron, are the solid state analog of the negatively charged hydrogen ion ͑H 2 ͒. Such systems are of great interest, to a large extent because their small electron effective mass and large dielectric constants allow one, at least in principle, to investigate the plenitude of magnetic bound states predicted for the H 2 ion at much higher (by .10 4 and, thus, inaccessible) fields. While there have been many reports of D 2 centers in III-V semiconductors during the past decade, most are for quantum well (QW) samples, where two-dimensional (2D) effects increase the D 2 binding energy. The handful of studies [1-3] dealing with D 2 in bulk materials all involve significant binding energy enhancements due to magnetic fields. These early far infrared (FIR) investigations, albeit the first to identify D 2 states in bulk GaAs, suffered from a combination of materials and experimental technique-related problems which strictly limited these studies to the observation of relatively broad D 2 bands in a restricted number of compensated samples.As a result of these difficulties, recent effort has been focused on the study of 2D D 2 states in QW geometries, which also offer the possibility of engineering appropriate conditions for the creation of D 2 centers, via selective doping techniques [4][5][6][7]. While this has allowed D 2 centers to be identified in a less restricted variety of materials, the linewidths associated with the D 2 transitions observed in all of the existing FIR studies are still very broad, especially in comparison to the very small binding energy expected for D 2 in bulk GaAs [ϳ3.7 K or 2.6 cm 21 , where the effective Rydberg for neutral donors in GaAs is taken to be R ‫ء‬ 46.09 cm 21 (5.715 meV) [8] ] [9,10]. Further complications arise during the interpretation of QW FIR absorption spectra due to the possibility of confusing D 2 features with those arising from interexcited state neutral impurity transitions (from both well and barrier materials), as well as cyclotron resonance. Hence, identification of D 2 features in a given FIR absorption spectrum is not straightforward, relying on comparisons with quantitative theoretical predictions, and has often been controversial [1,[4][5][6][7]11].Recent advances in the purity of e...

Characterization of high-purity arsine and gallium arsenide epilayers grown by MOCVD

“…We also note that there is a donor-carbon transition shoulder in both Samples 1 and 3 from 1.4916 eV (28.2 meV under the nearband emission) to 1.4925 eV (26.5 meV under the near-band emission) which indicates the transition (D 0 , C 0 ) and (D À , C 0 ) [30]. Since, very low temperature PL transitions involving D À singlet states in high-purity epitaxial GaAs [30,31] have been identified in the literature (the donor-carbon transition appears at about 1.4916 eV, and the negative donor-carbon transition is at about 1.4924 eV), (D À , C 0 ) in Sample 1 indicates high-purity GaAs.…”

“…Since, very low temperature PL transitions involving D À singlet states in high-purity epitaxial GaAs [30,31] have been identified in the literature (the donor-carbon transition appears at about 1.4916 eV, and the negative donor-carbon transition is at about 1.4924 eV), (D À , C 0 ) in Sample 1 indicates high-purity GaAs. In Fig.…”

Magnetophotoluminescence ofD−singlet and triplet states in GaAs

“…17 Under low-temperature and low-excitation conditions, this new transition can become the dominant radiative process, exhibiting linewidths on the order of 1 cm Ϫ1 . In this paper, we extend the previous study by reexamining this process in the presence of a magnetic field.…”

“…17 Figure 1 plots the photoluminescence spectra of the samples using an Ar ϩ laser excitation density of about 10 Ϫ2 W/cm 2 . The topmost spectra is from the high-quality MBE sample, and the ripples on the polariton feature are interference fringes as the polariton propagates between the surfaces of these thin, free-standing layers.…”

“…The temperatures of the He baths were determined by measuring the He vapor pressure. PL results were collected in the Faraday configuration using apparatus described earlier, 17 with incident power densities typically between 10 Ϫ4 and 10 Ϫ3 W/cm 2 at a wavelength of about 810 nm. Throughout this paper, binding energies will be presented in units of the effective Rydberg for neutral donors in GaAs, taken to be R*ϭ46.09 cm Ϫ1 ͑5.715 meV͒, 19 and magnetic-field values will be referred to in terms of the dimensionless parameter ␥ϭheB/4m*cR*, where m*, the electron effective mass for GaAs, is here taken to be 0.066 times the free-electron mass.…”