P. D. Dapkus

Carrier collection in a semiconductor quantum well

Data are presented showing that a GaAs quantum well, sandwiched between two epitaxial AlxGa1-xAs(x ∼ 0.4) confining layers, loses its effectiveness as a collector of excess carriers and as a source of recombination radiation for well dimensions Lz < 100 A. It is shown that this behavior is expected because of the difficulty in scattering carriers to the bottom of the quantum well as Lz → lp, the path length for scattering (LO phonon).

Temperature dependence of threshold current for quantum‐well AlxGa1−xAs‐GaAs heterostructure laser diodes

Data are presented showing that the threshold current density Jth(T) of quantum‐well AlxGa1−xAs‐GaAs heterostructure laser diodes, grown by MO‐CVD, is less temperature dependent than that of conventional DH lasers. T0 in the usual expression Jth∝exp(T/T0) can be high as 437 °C. This behavior is explained in terms of the steplike density of states and the disturbed electron and phonon distribution functions of the quantum‐well active region.

Temperature dependence of threshold current for a quantum-well heterostructure laser

Abstract The threshold current density, J th , of a quantum-well laser diode is calculated taking into account the quasi-two-dimensional nature of the heterostructure. The calculated value of J th ( T ) for a quantum-well laser diode is found, in agreement with experiment, to be less temperature sensitive than that of a conventional double heterojunction laser. The step-like densities of states and the perturbed (hot) carrier distribution of a quasi-two-dimensional structure are responsible for the weaker temperature dependence. Supporting data on quantum-well Al x Ga 1- x AsGaAs heterostructure laser diodes grown by MO-CVD are presented showing that in the conventional expression J th ( T ) = J th (0) exp ( T / T 0 ), T 0 can be as high as ∼ 437°C.

High‐efficiency GaAlAs/GaAs heterostructure solar cells grown by metalorganic chemical vapor deposition

High‐efficiency GaAlAs/GaAs heterostructure solar cells have been grown by metalorganic chemical vapor deposition (MO−CVD). Simulated air‐mass‐zero (AM0) short‐circuit current densities of 24.5 mA/cm2, open‐circuit voltages of 0.99 V, fill factors of 0.74, and efficiencies of 12.8% have been measured on devices without AR coatings (uncorrected for contact area). These cell structures employ a thin (∼520A) GaAlAs : Zn window and a GaAs : Zn/GaAs : Se p‐n junction grown entirely by the MO‐CVD process.

Phonon‐sideband MO‐CVD quantum‐well AlxGa1−xAs‐GaAs heterostructure laser

Laser operation (4.2–300 °K) of multiple‐quantum‐well AlxGa1−xAs‐GaAs heterostructures on a phonon (LO) sideband ∼36 meV below the lowest confined‐particle transitions is described. Phonon‐sideband laser data are presented on two different metalorganic chemical‐vapor‐deposited (MO‐CVD) quantum‐well heterostructures with four GaAs active regions (Lz∼50 and ∼90 A) coupled by three AlxGa1−xAs (x∼0.35) barriers.

Phonon‐assisted recombination and stimulated emission in quantum‐well AlxGa1−xAs‐GaAs heterostructures

Extensive data are presented on various photopumped multiple‐quantum‐well AlxGa1−x As‐GaAs heterostructures, grown by metalorganic chemical vapor deposition, showing the variety of laser operation that can be observed one and two phonons below the lowest (n=1, n′=1′) confined‐particle electron‐to‐heavy‐hole (e→hh, n) and electron‐to‐light‐hole (e→lh, n′) recombination transitions. These experiments are performed on small cleaved rectangular samples that, because of two identifiable sets of orthogonal coupled modes, permit unambiguous identification of laser operation on LO‐phonon sidebands below the confined‐particle transitions. For a small number (two) of closely coupled (∼50 A) GaAs quantum wells of size Lz ∼50 A laser operation occurs on multiples of h/ωLO from one phonon below transition n=1 (E1) to within a phonon or two of the L indirect band edge. AlxGa1−x As‐GaAs heterostructures with more coupled GaAs quantum wells readily permit observation of laser operation two phonons below the lowest confin...

Continuous 300 °K laser operation of single‐quantum‐well AlxGa1−xAs‐GaAs heterostructure diodes grown by metalorganic chemical vapor deposition

Stripe‐geometry single‐quantum‐well AlxGa1−xAs‐GaAs double‐heterostructure laser diodes (Lz∼200 A) grown by metalorganic chemical vapor deposition are shown to operate continuously at 300 °K on the first (n=1) electron–to–heavy–hole (e→hh) or first (n′=1′) electron–to–light–hole (e→lh) confined‐particle transitions (h/ω−Eg∼11 meV). These laser diodes exhibit an external differential quantum efficiency as high as ηext∼80% (output power 5.4 mW at 65 mA drive current).

Electrical properties of polycrystalline GaAs films

Electrical properties of Se‐ and Zn‐doped polycrystalline GaAs deposited by metalorganic chemical vapor deposition on substrates of polycrystalline alumina and glass were investigated. Hall‐effect and resistivity measurements were made over a wide range of temperature (77–420 K). The electrical activation energies were found by measuring the variation of resistivity and carrier mobility of the polycrystalline GaAs films with sample temperature. The resistivity and mobility were found to be temperature activated over a wide temperature range as exp(Eb /kT) and exp(−Eb /kT), respectively, with the same activation energy applying to both properties. The results have been interpreted in terms of a modified grain boundary trapping model.

Al0.5Ga0.5As‐GaAs heterojunction phototransistors grown by metalorganic chemical vapor deposition

Al0.5Ga0.5As/GaAs heterojunction phototransistors have been fabricated from structures grown by the MO‐CVD process. The relatively high optical gains (∼100) and short response times (≲2 nsec) obtained with these devices indicate that an optimized AlxGa1−xAs/GaAs heterostructure phototransistor could be a suitable detector for optical‐fiber‐communication systems using GaAs DH lasers.

Bandfilling in metalorganic chemical vapor deposited AlxGa1−xAs‐GaAs‐AlxGa1−xAs quantum‐well heterostructure lasers

Data are presented showing that quantum‐well (Lz∼200 A) AlxGa1−xAs‐GaAs‐AlxGa1−xAs heterostructures, grown by metalorganic chemical vapor deposition, can be operated as lasers on confined‐particle transitions over an unusually large range (Δλ≳1000 A). The bandfilling properties of these quantum‐well heterostructures, which can easily be excited to carrier densities as high as n≳1019/cm3, are described. Quantum‐well laser diodes (x∼0.5) are described that operate (300 K) from the Γ band edge to wavelengths as short as 7700 A (ΔE∼185 meV). Narrow photopumped samples (15–30 μm) are shown to operate (77 K) as lasers on clearly defined confined‐particle transitions from the band edge to 6980 A (ΔE∼270 meV). On samples from another wafer, laser operation has been observed to 6885 A (ΔE≡hν−Eg=293 meV). The photoluminescence spectra of these heterostructures extend well into the region of the recently determined L band minima of GaAs.