D. A. Kleinman

Strong 8.2 μm infrared intersubband absorption in doped GaAs/AlAs quantum well waveguides

We have measured the infrared intersubband absorption at 8.2 μm in doped GaAs/AlAs quantum well superlattices. Waveguide geometry experiments demonstrate strong absorption with 95% of the incident infrared energy being absorbed.

InGaAs/InAlAs multiquantum well intersubband absorption at a wavelength of λ=4.4 μm

We report, for the first time, intersubband absorption experiments in doped InGaAs/InAlAs multiquantum well superlattices and observe a resonance peak at a wavelength of λ=4.4 μm which is in good agreement with theory. This material system may be useful for detectors in the λ=3–5 μm spectral region.

New transitions in the photoluminescence of GaAs quantum wells

When GaAs quantum wells are optically excited with intensities ≳10 kW/cm2 new peaks appear in the photoluminescence spectrum at low temperatures. The excitation spectra are used to demonstrate that the new peaks correspond to the recombination of electrons in excited well states, n≳1, with holes in n = 1 states. These parity‐forbidden transitions, Δn odd, derive their strength from three body interactions that occur at high excitation levels.

Parabolic quantum wells with the GaAs-Al x Ga1−x As system

Photoluminescence measurements at 5 K on wafers containing parabolic quantum wells fabricated by molecular-beam epitaxy with the GaAs-AI0.3Ga0.7As system reflect harmonic oscillator-like electron and hole levels. The many observed heavy-hole transitions can be fitted accurately with a model that divides the energy-gap discontinuity ΔE g equally between the conduction and valence-band wells. This is in marked contrast to the usual ΔE c = 0.85ΔE g and ΔE v = 0.15ΔE g generally assumed for square wells. Experiment and theory show that parabolic wells can lead to parity-allowed Δn = 2 (“forbidden”) transitions with strengths greater than Of nearby Δn = 0(“allowed”) transitions.

Measurement of high electron drift velocity in a submicron, heavily doped graded gap AlxGa1−xAs layer

We have directly determined a high velocity (v=2×107 cm/s) for electrons in a submicron (0.42 μm), strongly graded (quasifield F=8.8 kV/cm) highly doped ( p=4×1018 cm−3) AlxGa1−xAs layer. A transit time of only 1.7 ps was measured (an order of magnitude shorter than that for F=1.2 kV/cm). Such a structure would be ideal for the low resistance base of a high‐speed n‐p‐n transistor.

Two‐photon absorption of Nd laser radiation in GaAs

The two‐photon absorption coefficient of GaAs at 1.32 μm is found to be 0.033 ± 0.015 cm/MW. This value was obtained from transmission measurements employing a Q‐switched Nd–YAG laser and an improved theoretical analysis taking into account fluctuations and the Gaussian pulse shape. Evidence of thermal self‐focusing was seen in samples with linear absorption coefficients of order 1 cm−1 or larger.

Observation of doubly resonant LO-phonon Raman scattering with GaAs-Alx Ga1−x As quantum wells

Abstract LO-phonon Ramsn scattering has been observed with GaAs quantum wells where the incident and scattered photon energies are both resonant with an exciton transition. This very strong single phonon intrinsic effect, called “doubly resonant Raman scattering” (DRRS), does not exist in intrinsic bulk GaAs. The largest DRRS was observed with the scattered photon at the n=1 heavy hole free exciton E1h and incident photon at the nominally forbidden transition involving the n=1 electron and n=3 heavy hole E13h when E 1h + h ;ω LO = E 13h where h ω LO = 36.7 meV is the LO-phonon frequency of GaAs. The sharp DRRS line for the principal sample studied has nearly three times the circular polarization of the broad ordinary luminescence and a large linear polarization (optical alignment) not usually seen in the luminescence of quantum wells. From a theoretical treatment for the first order DRRS, it is concluded that the Frohlich interaction can account for the observed strength and that as expected the deformation potential contribution is negligible. Also, relaxation effects are identified in these Raman spectra.

Vibration‐induced modulation of fiberguide transmission

Linear intensity modulation of several percent in fiberguide transmission caused by flexural vibrations has been observed in bent fiberguides and attributed to modulated bending loss. Measurements of bending loss are presented which support this interpretation.