K. E. Kudryavtsev

Efficient long wavelength interband photoluminescence from HgCdTe epitaxial films at wavelengths up to 26 μm

Photoluminescence (PL) and photoconductivity (PC) studies of Hg1−xCdxTe (0.19 ≤ x ≤ 0.23) epitaxial films are presented. Interband PL is observed at wavelengths from 26 to 6 μm and in the temperature range 18 K–200 K. The PL line full width at half maximum is about 6 meV (4kT) at 18 K and approaches its theoretical limit of 1.8kT at higher temperatures. Carrier recombination process is also investigated by time resolved studies of PL and PC at pulsed excitation. Radiative transitions are shown to be the dominating mechanism of carrier recombination at high excitation levels.

Spectra and kinetics of THz photoconductivity in narrow-gap Hg1?xCdxTe (x < 0.2) epitaxial films

Investigation into far infrared photoconductivity (PC) in narrow-gap epitaxial bulk Hg1–xCdxTe (x < 0.2) films grown by molecular beam epitaxy and chemical vapor deposition techniques is presented. A broadband of photosensitivity in terahertz region is found at 4.2 and 77 K. Some long-wavelength peculiarities of spectra are discovered and their origins are discussed. We also study PC relaxation process with nanosecond time resolution. It is found that carrier relaxation is non-radiative and measured lifetimes show that some of the structures are applicable for detecting in very long-wavelength infrared range.

SiGe nanostructures with self-assembled islands for Si-based optoelectronics

The effect of structure parameters on the electroluminescence and photoconductivity of multilayer structures with self-assembled Ge(Si)/Si(0 0 1) islands has been studied. The highest intensity of the room-temperature electroluminescence in the wavelength range of 1.3–1.55 µm has been observed for the islands grown at 600 °C. The same diode structures with Ge(Si)/Si(0 0 1) islands have demonstrated room-temperature photoconductivity signals in the wavelength range of 1.3–1.55 µm. The observed overlap of the electroluminescence and photoconductivity spectra obtained for the same structures with Ge(Si) islands makes these structures a promising material for the fabrication of a Si-based optocoupler. Less degradation after neutron irradiation has been observed for the electroluminescence and photoconductivity signals from multilayer structures with Ge(Si) self-assembled islands in comparison with bulk silicon structures. This result is associated with more effective confinement of charge carriers in the multilayer structures with Ge(Si) islands.

Time resolved photoluminescence spectroscopy of narrow gap Hg1−xCdxTe/CdyHg1−yTe quantum well heterostructures

Photoluminescence (PL) spectra and kinetics of narrow gap Hg1−xCdxTe/CdyHg1−yTe quantum well (QW) heterostructures grown by molecular beam epitaxy technique are studied. Interband PL spectra are observed from 18 K up to the room temperature. Time resolved studies reveal an additional PL line with slow kinetics (7 μs at 18 K) related to deep defect states in barrier layers. These states act as traps counteracting carrier injection into QWs. The decay time of PL signal from QW layers is about 5 μs showing that gain can be achieved at wavelengths 10–20 μm by placing such QWs in HgCdTe structures with waveguides.

Monolithically integrated InGaAs/GaAs/AlGaAs quantum well laser grown by MOCVD on exact Ge/Si(001) substrate

We report on realization of the InGaAs/GaAs/AlGaAs quantum well laser grown by metallorganic chemical vapor deposition on a virtual Ge-on-Si(001) substrate. The Ge buffer layer has been grown on a nominal Si(001) substrate by solid-source molecular beam epitaxy. Such Ge buffer possessed rather good crystalline quality and smooth surface and so provided the subsequent growth of the high-quality A3B5 laser structure. The laser operation has been demonstrated under electrical pumping at 77 K in the continuous wave mode and at room temperature in the pulsed mode. The emission wavelengths of 941 nm and 992 nm have been obtained at 77 K and 300 K, respectively. The corresponding threshold current densities were estimated as 463 A/cm2 at 77 K and 5.5 kA/cm2 at 300 K.

Long wavelength stimulated emission up to 9.5 μm from HgCdTe quantum well heterostructures

Stimulated emission from waveguide HgCdTe structures with several quantum wells inside waveguide core is demonstrated at wavelengths up to 9.5 μm. Photoluminescence line narrowing down to kT energy, as well as superlinear rise in its intensity evidence the onset of the stimulated emission, which takes place under optical pumping with intensity as small as ∼0.1 kW/cm2 at 18 K and 1 kW/cm2 at 80 K. One can conclude that HgCdTe structures potential for long-wavelength lasers is not exhausted.

Features of impurity-photoconductivity relaxation in boron-doped silicon

A series of studies of the impurity-photoconductivity relaxation in Si:B is carried out under pulse optical excitation by a narrow-band tunable radiation source in low and “heating” (10–500 V/cm) electric fields. It is shown that the dependence of the carrier-capture time in a band on the applied electric field is nonmonotonic and, in high fields (>75 V/cm), the capture time decreases with increasing field intensity, which is related to initiating the relaxation processes with optical-phonon emission within the band. The dependence of the relaxation rate for the carriers on the excitation-radiation wavelength is investigated, and a decrease in the carrier-capture time in the band is revealed in the vicinity of the Breit-Wigner-Fano resonances caused by direct capture at an impurity with optical-phonon emission.

Effect of parameters of Ge(Si)/Si(001) self-assembled islands on their electroluminescence at room temperature

The electroluminescence (EL) of multilayered p-i-n structures with the self-assembled Ge(Si)/Si(001) islands are investigated. It is found that the structures with islands grown at 600°C have the highest intensity of the electroluminescence signal at room temperature in the wavelength range of 1.3–1.55 μm. The annealing of structures with the Ge(Si) islands leads to an increase in the EL-signal intensity at low temperatures and hampers the temperature stability of this signal, which is related to the additional Si diffusion into islands during annealing. The found considerable increase in the electroluminescence-signal intensity with the thickness of the separating Si layer is associated with a decrease in the elastic stresses in the structure with an increase in this layer’s thickness. The highest EL quantum efficiency in the wavelength range of 1.3–1.55 μm obtained in investigated structures amounted to 0.01% at room temperature.

Comparative analysis of photoluminescence and electroluminescence of multilayer structures with self-assembled Ge(Si)/Si(001) island

Comparative studies of the photoluminescence and electroluminescence of multilayer structures with self-assembled Ge(Si)/Si(001) islands are carried out. The luminescence signal from the islands is observable up to room temperature. Annealing of the structures induces a shift of the luminescence peak to shorter wavelengths. The shift is temperature dependent, making possible controllable variations in the spectral position of the luminescence peak of the Ge(Si) islands in the range from 1.3 to 1.55 μm. The enhancement of the temperature quenching of photoluminescence of the islands with increasing annealing temperature is attributed to the decrease in the Ge content in the islands during annealing and, as a result, to a decrease in the depth of the potential well for holes in the islands. The well-pronounced suppression of the temperature quenching of electroluminescence of the Ge(Si) islands in the unannealed structure with increasing pumping current is demonstrated.

Long wavelength superluminescence from narrow gap HgCdTe epilayer at 100 K

Experimental evidence of long wavelength superluminescence (SL), i.e., amplification of spontaneous emission, in narrow gap HgCdTe bulk epitaxial film at 100 K is reported. Photoluminescence line narrowing is observed at 8.4 μm as pump power increases. However, plasmonic contribution to dielectric function is shown to be detrimental for light confinement at high pumping intensities, limiting the SL line intensity growth. The design of the structures optimal for obtaining stimulated emission in 10–36 μm range is further discussed.