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The development of new technology, which would be able to shift photosensitivity of Si devices to the mid-infrared range, preserving the benefits of cheap silicon readout circuits, is of high priority for short-wave infrared photo-detection in defense, medical, night vision, and material production applications. Group IV GeSn-based materials have recently shown promising optoelectronic characteristics, allowing extension of the detection range to the mid-infrared region. However, the electronic properties of the material are not well understood and need further research. In this work, we provide temperature dependent studies of carrier lifetime, diffusion coefficient, and diffusion length in Ge0.95Sn0.05 epilayer on silicon by applying contactless light induced transient grating technique. The observed temperature dependence of lifetime was explained by the recombination of carriers on vacancy-related defects. The electron and hole capture cross sections were calculated. The temperature dependence of the diffusion coefficient indicated hole mobility limited by phonon and defect scattering. Weakly temperature dependent diffusion length of ∼0.5 μm verified material suitability for efficient submicrometer-thick optoelectronic devices.

Recently, a novel method for evaluation of recombination coefficients corresponding to Shockley-Read-Hall, radiative, and Auger recombination channels has been proposed, which combines measurements of the light emitting diode (LED) external quantum efficiency under continuous wave operation with the determination of non-equilibrium carrier differential life time (DLT) by small-signal time-resolved photoluminescence [Nippert et al., Jpn. J. Appl. Phys., Part 1 55, 05FJ01 (2016)]. In this work, we suggest an alternative technique, small-signal frequency-domain lifetime measurements, which is implemented more easily and capable of operating in a wider range of LED operating currents. The DLTs measured by both techniques are shown to agree well with each other, but saturate at low currents, contrary to the trend predicted by the well-known ABC-model. We discuss possible reasons for this deviation, as well as advantages and limitations of the measurement techniques.

After epitaxial growth of GaN on Si(100) substrates using an Er2O3 interlayer, two dominant growth orientations can be observed: semi-polar (101¯3) as well as non-polar (112¯0). Epilayers with the (101¯3) orientation lead to the formation of truncated pyramids, which were studied in detail by high-resolution X-ray diffraction, photoluminescence, and scanning electron microscopy (SEM). Depending on the GaN growth orientation and in-plane relation to the Er2O3 interlayer, lattice mismatches in the growth plane were calculated. In order to understand the formation of truncated pyramids, a method for facet identification from SEM images under different tilt angles was developed. This method was used to reconstruct truncated pyramids from our experiments. These were then compared with calculations of the corresponding kinetic Wulff construction, to explain the preferential growth of (101¯3) GaN.

Time-resolved nondegenerate four-wave mixing experiments were performed on 2.6-μm-thick GaN epilayers grown by metalorganic chemical-vapor deposition using picosecond pulses at 355 and 1064 nm for grating recording and probing, respectively. Measurements of free carrier grating kinetics at various grating periods Λ in range from 3 to 10 μm allowed determination of nonequilibrium carrier bipolar diffusion coefficient D=1.7 cm2/s at 300 K. Substitution of the D value into two-dimensional carrier transport model allowed fitting of the whole set of grating kinetics at various Λ varying surface recombination velocity S and linear recombination time τR. This procedure provided us a value of S=5×104 cm/s as well as carrier lifetime of ∼1 ns.

Carrier dynamics in highly excited InN epitaxial layers was investigated in the 1550–2440 nm (0.8–0.51 eV) spectral range by using a femtosecond differential transmission technique. A transition from induced bleaching to induced absorption was observed for probing energy of 90 meV below the bandgap of the samples. The decay of the induced free carrier absorption provided the averaged lifetime of the total nonequilibrium carriers. In the carrier density range of Δn=1018–1020 cm−3, the density-dependent recombination mechanism was attributed to trap-assisted Auger recombination with decay rate 1/τ=BTAARΔn, with BTAAR in the range (4–30)×10−10 cm3 s−1 for layers with different defect densities.

Variable temperature light-induced transient grating technique combined with electron beam-induced current measurements in situ in a scanning electron microscope were employed for carrier transport studies in quasibulk hydride-vapor phase epitaxy grown undoped GaN layers. Diffusion length of carriers independently determined from both techniques was found to increase with temperature in the range from 70 to 400 K. This increase was attributed to the temperature-induced growth of carrier lifetime, as was confirmed by light-induced transient grating measurements below 300 K and by cathodoluminescence above room temperature.

A holographic beam splitter has been integrated into a picosecond four-wave mixing (FWM) scheme. This modification significantly simplified the procedure of dynamic grating recording, thus making the FWM technique an easy-to-use tool for the holographic characterization of wide band gap materials. The novel FWM scheme was applied for characterization of hydride vapor phase epitaxy-grown undoped GaN layers of different thickness. It allowed the determination of carrier lifetime, diffusion coefficient, and carrier diffusion length by optical means, as well as the study of carrier recombination peculiarities with respect to dislocation and excess carrier density.

Optical monitoring of nonequilibrium carrier dynamics was performed in freestanding GaN. Four-wave mixing kinetics directly provided carrier lifetime of 5.4ns in the layer, while complementary measurements by photoluminescence technique revealed the fast transients with subnanosecond decay time. Numerical modeling of photoluminescence decay taking into account the carrier spatial-temporal dynamics allowed us to attribute an origin of the fast photoluminescence transients to carrier diffusion to the bulk and to reabsorption of the backward emission. The studies demonstrated carrier diffusion limited applicability of the time-resolved photoluminescence technique for carrier lifetime measurements in a high quality thick III-nitride layers.