Nodestructive optical methods, based on measurements of the 'plasma edge' and the Moss-Burstein shift, are investigated as contactless reflection and transmission spectra of undoped and Sidoped lnAs grown on GaAs by MBE are studied. A curve-fitting procedure is developed to fit the reflectivity spectra with or without phonon-plasmon coupling. The range of carrier concentrations over which these optical methods can provide useful characterization is evaluated. The effective mass determined from 'plasma edge' measurements agrees well with the simple Kane model for n below 2.7 x 10'' c t r 3 . For n above 4 x I O ' ' cm-3, the sample effective mass deviates considerably from the simple Kane model. Excitonic structure in the absorption edge is reported for high-purity undoped samples.

A midinfrared picosecond spectrometer based on an Er + laser-pumped optical parametric generator has been used to study Auger recombination processes in intrinsic InSb at room temperature. After carrier excitation by a 100-psec A, =2.8 pm Er'+ laser pulse the sample transmission change due to excess carriers was probed, using short pulses of wavelengths varying in the range 4 -6 pm, as a function of time delay. It was shown that over the measured range of carrier densities (n =10' -10' cm ) the momentum-conserving conduction -heavy-hole -heavy-hole -light-hole Auger process was the predominant channel for electron-hole recombination with a quadratic rather than a cubic dependence of recombination rate on carrier density. The effective Auger lifetime scales as~A "g = C2n withCz=7.4(+1.5) X10 cm s '. This type of carrier concentration dependence is in accordance with theoretical predictions for semiconductors in which the electron component of the carrier population is degenerate.

Room-temperature pump–probe transmission experiments have been performed on an arsenic-rich InAs/InAs1−xSbx strained layer superlattice (SLS) above the fundamental absorption edge near 10 μm, using a ps far-infrared free-electron laser. Measurements show complete bleaching at the excitation frequency, with recovery times which are found to be strongly dependent on the pump photon energy. At high excited carrier densities, corresponding to high photon energy and interband absorption coefficient, the recombination is dominated by Auger processes. A direct comparison with identical measurements on epilayers of InSb, of comparable room-temperature band gap, shows that the Auger processes have been substantially suppressed in the superlattice case as a result of both the quantum confinement and strain splittings in the SLS structure. In the nondegenerate regime, where the Auger lifetime scales as τ−1aug=C1N2e, a value of C1 some 100 times smaller is obtained for the SLS structure. The results have been interpreted in terms of an 8×8 k⋅p SLS energy band calculation, including the full dispersion for both k in plane and k parallel to the growth direction. This is the strongest example of room-temperature Auger suppression observed to date for these long-wavelength SLS alloy compositions and implies that these SLS materials may be attractive for applications as room-temperature mid-IR diode lasers.

Molecular beam epitaxial growth of a normally homogeneous InAs0.5Sb0.5 alloy below 430 °C results in its coherent phase separation into platelets of two different alloy compositions with tetragonally distorted crystal lattices. This produces a ‘‘natural’’ strained layer superlattice (n-SLS) with clearly defined interfaces modulated in the [001] growth direction. A description of the n-SLS growth mode in InAsSb is outlined, and the optical response of a n-SLS structure, which extends to 12.5 μm−considerably further than that of a homogeneous InAs0.5Sb0.5 layer (8.9 μm)−is reported.

Room-temperature InAs/InAs1−xSbx strained-layer superlattice light-emitting diodes (x∼8%) are reported that emit at λ∼4.2 μm with an internal efficiency of 2.8%. The structures are grown by molecular beam epitaxy on slightly mismatched InAs substrates and include a strained AlSb barrier layer to prevent electron migration to the dislocated substrate–epilayer interface region. Comparison with a near identical structure grown without the barrier layer indicates a factor of four improvement in device efficiency at room temperature.

A theoretical framework for the design of asymmetrically doped n-type n-i-p-i- superlattices for subband detector applications in the 10 μm spectral range is described. Excellent agreement is found with the subband absorption spectra measured in a series of GaAs n-type n-i-p-i- samples and oscillator strengths, transition energies, and dipole matrix elements comparable with conventional quantum-well heterostructure detectors are found. Pronounced IR-absorption modulation by optical pumping with band-gap radiation is seen, due to the enhanced interband recombination time resulting from the type-II n-i-p-i- potential. The prospective advantages of n-type n-i-p-i- devices for the detection and modulation of 10 μm radiation are discussed.

Temperature-and excitation-dependent photoluminescence measurements have been carried out on 0.7-5 um thick heteroepitaxial InAs layers grown by molecular beam epitaxy (MBE). Excitonic photoluminescence with linewidths down to 5 meV reveals t h e high optical quality of t h e epilayers despite t h e 7",,, mismatch between the lnAs and the GaAs substrates. Peaks at 403 and 391 meV, which quench rapidly with increasing temperature, are attributed to bound excitons, and a sharp (7 meV FWHM) intense line at 417 meV is tentatively attributed to free excitonic recombination. A broad 18 meV wide band (peaking at 378 meV) which blue shifts with increasing excitation. characteristic of a donor-acceptor pair transition band, is reported for the first time in InAs.

We have measured the in-plane ambipolar diffusion constant in a heterou s to monitor the time evolution of an excess carrier population at any point on the sample without the need for electrical contacts. The diffusion is found to be enhanced by almost an order of magnitude over that i n bulk material (to values of 45cm2 s-') due to the 'giant ambipolar diffusion' mechanism arising from perturbations to the periodic nipi potential. This has important implications in the switching across an individual pixel in a device where the in-piane diffusion dynamics are typically the limiting factor in the switching speed. nipi reff!ection m&u!ator using a noye! a!i-optirdi technique. This techn!que a!io\ws "50 of nip; s!r:cc!!res 2s fast optical Swjtching 25 it eps~res cgifor,~