Inhomogeneous Line Broadening in Donor Magneto-Optical Spectra

Larsen, David M.

doi:10.1103/physrevb.8.535

Cited by 120 publications

(31 citation statements)

References 10 publications

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“…The techniques of high resolution far-infrared Fourier spectroscopy [1,2,3] as well as far-infrared laser magnetospectroscopy [4] have been applied yielding detailed knowledge of donor levels in a wide range of magnetic field strengths. Since the early work of Larsen [5] many variational calculations based on the effective mass approximation have been performed reproducing the bound donor levels in excellent agreement with experimental results [6].…”

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confidence: 57%

Metastable shallow donor states of n-GaAs in a magnetic field

Wagner

Prettl

1988

Solid State Communications

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The photothermal spectrum of shallow donors in n-GaAs has been investigated at various magnetic field strengths up to 4T at different temperatures between 1.4 and 12K. Weak spectral structures observed at frequencies above the dominant ls --~ 2p+1 line are attributed to optical excitations into metastable states which arise in a magnetic field. The final states of these transitions can be unambiguously assigned by using high field quantum numbers.The optical excitation spectra of hydrogen-like shallow donors in high purity GaAs epitaxial layers have been studied extensively in the past by photothermal ionisation spectroscopy. The techniques of high resolution far-infrared Fourier spectroscopy [1,2,3] as well as far-infrared laser magnetospectroscopy [4] have been applied yielding detailed knowledge of donor levels in a wide range of magnetic field strengths. Since the early work of Larsen [5] many variational calculations based on the effective mass approximation have been performed reproducing the bound donor levels in excellent agreement with experimental results [6].The most prominent lines observed in photoconductivity spectra at low temperatures correspond to transitions from the ls donor ground state to 2p:1:1 states where nlm is the low field hydrogen atom energy level notation. Besides these strong lines, weak transitions like ls --~ 2s are observed violating the electric dipole selection rules. This effect is attributed to admixing of p-states due to the Stark effect caused by the strong electric fields of ionized impurities in the partially compensated material. The photoconductivity spectra of n-GaAs in a magnetic field contain, however, additional weak structures which have not yet been identified. In the present study we show that most of these lines, being observed in Faraday configuration, may be grouped in pairs with frequency separation ~:c, where v:c = eB/m* is the conduction band cyclotron frequency. Taking into account electric dipole selection rules Am : ±1 and 7riTrf : -1, where 7ri,j" are the parities of the initial and final states respectively, we conclude that most of the observed structures are due to excitation of metastable states from the donor ground state. Metastable states arise in a magnetic field out of the donor continuum and do not lead to donor bound states in the zero field limit. The final states may be assigned by high field quantum numbers (N,m,t¢) where N and m denote the Landau levels and the angular momentum respectively and counts the donor states below each (N, m) Landau subband. The parity of a state in the high field notation is given by ~r = (-1)m+'L The measurements were carried out on an n-GaAs epitaxial layer of 41/~m thickness predominantly containing silicon shallow donors with an effective concentration N D -NA = 9.2 • 1013 cm -3, The mobility at liquid nitrogen temperature was/z = 9.4.104 cm2/Vs. Ohmic point contacts were alloyed at opposite edges of the layer and a wedged piece of polished semiinsulating GaAs was glued with paraffin oil onto the substrate...

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confidence: 57%

Metastable shallow donor states of n-GaAs in a magnetic field

Wagner

Prettl

1988

Solid State Communications

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“…The magnetic field dependence of donor energy levels was calculated by Larsen [9] and experimentally verified by many investigations [10]. Since the photon energy at 20.2 cm -1 is too small to cause optical transitions between the l s donor ground state and excited states at any magnetic field, positive photoconductivity at this frequency must result from photoionization from excited donor states.…”

Section: C) Discussionmentioning

confidence: 99%

“…(1)- (4). From (4) one obtains in the steady state (9) From (2) and (7) it follows: T*(P A-n-na) (10) no-T,+Xln X I n(e A -n -nl) (11) riD* = T* + X 1 n…”

Section: Theory A) Generation-recombination Modelmentioning

confidence: 99%

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Impact ionization induced negative far-infrared photoconductivity inn-GaAs

Schöll

Heisel

Prettl

1982

Z. Physik B - Condensed Matter

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Far-infrared photoconductivity of n-GaAs epitaxial layers showing impact ionization breakdown has been investigated by molecular lasers at photon energies below the 1 s -2p shallow donor transition energy. Negative photoconductivity was observed if a magnetic field was applied to the crystals and if impact ionization of donors by the electric bias field was the dominant electron excitation mechanism. The experimental results are qualitatively explained on the basis of the generation-recombination kinetics of electrons bound to donors. Negative photoconductivity is attributed to optically induced free to bound transitions of electrons from the N=0 Landau band to donor levels shifted by the magnetic field above the low energy edge of the conduction band.

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“…In bulk GaAs these line widths can be reduced by the application of an external magnetic field. 9 It was the anticipation that a similar technique would be used in these quantum well structures that led to the investigation of the Zeeman levels of shallow donors and Wannier exciton in quantum wells.…”

Section: I1mentioning

confidence: 99%

Zeeman Studies of Shallow Donors and Excitons in Quantum Wells.

Greene¹

1984

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Inhomogeneous Line Broadening in Donor Magneto-Optical Spectra

Cited by 120 publications

References 10 publications

Metastable shallow donor states of n-GaAs in a magnetic field

Metastable shallow donor states of n-GaAs in a magnetic field

Impact ionization induced negative far-infrared photoconductivity inn-GaAs

Zeeman Studies of Shallow Donors and Excitons in Quantum Wells.

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