N. L. Bazhenov

Photoluminescence of Hg1 − xCdxTe based heterostructures grown by molecular-beam epitaxy

Photoluminescence (PL) of Hg1 − xCdxTe-based heterostructures grown by molecular-beam epitaxy (MBE) on GaAs and Si substrates has been studied. It is shown that a pronounced disruption of the long-range order in the crystal lattice is characteristic of structures of this kind. It is demonstrated that the observed disordering is mostly due to the nonequilibrium nature of MBE and can be partly eliminated by postgrowth thermal annealing. Low-temperature spectra of epitaxial layers and structures with wide potential wells are dominated by the recombination peak of an exciton localized in density-of-states tails; the energy of this peak is substantially lower than the energy gap. In quantum-well (QW) structures at low temperatures, the main PL peak is due to carrier recombination between QW levels and the energy of the emitted photon is strictly determined by the effective (with the QW levels taken into account) energy gap.

Temperature dependence of the threshold current of QW lasers

The temperature dependence of the threshold current in GaInAs-based laser structures has been studied in a wide temperature range (4.2 ≤ T ≤ 290 K). It is shown that this dependence is monotonic in the entire temperature interval studied. Theoretical expressions for the threshold carrier density are derived and it is demonstrated that this density depends on temperature linearly. It is shown that the main contribution to the threshold current comes from monomolecular (Shockley-Read) recombination at low temperatures. At T > 77 K, the threshold current is determined by radiative recombination. At higher temperatures, close to room temperature, Auger recombination also makes a contribution. The threshold current grows with temperature linearly in the case of radiative recombination and in accordance with T3 in the case of Auger recombination.

Electrical and optical properties of CdHgTe films grown by molecular-beam epitaxy on silicon substrates

The electrical and optical properties of epitaxial CdHgTe films grown on silicon substrates by molecular-beam epitaxy have been studied. The results of photoluminescence measurements are indicative of the high structural perfection of the films, and Hall data combined with low-energy ion treatment point to a low concentration of residual donors (∼5 × 1014 cm−3). Acceptor states supposedly related to the capture of impurities at structural defects typical of strongly lattice-mismatched heteroepitaxial structures are found in the films.

Acceptor states in heteroepitaxial CdHgTe films grown by molecular-beam epitaxy

The photoluminescence method is used to study acceptor states in CdHgTe heteroepitaxial films (HEFs) grown by molecular-beam epitaxy. A comparison of the photoluminescence spectra of HEFs grown on GaAs substrates (CdHgTe/GaAs) with the spectra of CdHgTe/Si HEFs demonstrates that acceptor states with energy depths of about 18 and 27 meV are specific to CdHgTe/GaAs HEFs. The possible nature of these states and its relation to the HEF synthesis conditions and, in particular, to the vacancy doping occurring under conditions of a mercury deficiency during the course of epitaxy and postgrowth processing are discussed.

Defects in heteroepitaxial CdHgTe/Si layers and their behavior under conditions of implanted p + - n photodiode structure formation

The impurity-defect structure of heteroepitaxial CdxHg1 − xTe/Si (0.35 < x < 0.39) layers grown by molecular beam epitaxy for the creation of arsenic-ion-implanted p+-n junctions has been studied by the photoluminescence method. It is established that full realization of the possibilities of p+-on-n photodiode structures based on the CdHgTe/Si system is hindered by uncontrolled doping of the material that leads to the formation of both shallow (impurity level energy ∼10 meV) and deep (∼50 meV) acceptor levels.

High-temperature photoluminescence of CdHgTe solid solutions grown by molecular-beam epitaxy

The spectra of the high-temperature (up to 300 K) photoluminescence of the heteroepitaxial structures based on the CdHgTe solid solutions that are grown using molecular-beam epitaxy and emit at room temperature in the wavelength interval λ = 1.5–4.3 μm are analyzed. It is demonstrated that the observed photoluminescence of the CdHgTe narrow-gap semiconductor at high temperatures and the specific features of the high-temperature spectra can be interpreted using the disorder of the solid solution as in the case of the solid solutions of the group-III nitrides.

Effect of annealing on the optical and photoelectrical properties of CdxHg1 − xTe heteroepitaxial structures for the middle infrared range

We have studied the influence of various postgrowth treatments (annealing in helium atmosphere or mercury vapor, low-energy ion etching) on the optical and photoelectrical properties of mercury cadmium telluride (CdxHg1 − xTe) heteroepitaxial structures for the photo- and optoelectronic devices operating in the middle infrared range (3–5 μm). It is established that the annealing in mercury vapor is optimum for improving the photoluminescence characteristics in this range.

Temperature dependence of the carrier lifetime in narrow-gap CdxHg1–xTe solid solutions: Radiative recombination

The probability of the radiative recombination of carriers in narrow-gap semiconductors is analyzed for the example of CdxHg1–xTe solid solutions. Expressions are derived for the imaginary part of the dielectric permittivity in terms of the three-band Kane’s model with consideration for the nonparabolic dependence of the carrier energy on the wave vector. It is shown that taking into account this nonparabolicity of the energy spectrum of carriers modifies the dependence of the imaginary part of the dielectric permittivity on frequency. Expressions for the probability of radiative recombination, derived in terms of the simple parabolic model and Kane’s model with and without the nonparabolicity effect taken into account, are compared. It is shown that the contributions to recombination from electron transitions to heavy- and light-hole bands are close and the contribution from light holes cannot be neglected when calculating the radiative-recombination probability.

Photoluminescence of CdHgTe solid solutions subjected to low-energy ion treatment

The photoluminescence (PL) of CdHgTe solid solutions subjected to low-energy ion treatment is studied. A blue shift of the peaks in the PL spectra is observed immediately after ion treatment, which is attributed to the formation of a high concentration of donor defects and to the Burstein-Moss effect. The change in the shape of the PL spectra and, in particular, the disappearance of lines associated with transitions to acceptor states indicate that these defects are formed by the interaction of interstitial mercury atoms introduced into the sample during the course of treatment with impurity atoms. As the treatment is terminated, the electron concentration decreases due to the disintegration of defects and the blue shift disappears, but the shape of the spectra remains unchanged. This behavior of the PL spectra can be used for diagnostics of the defect-impurity structure of CdHgTe.

Photoluminescence of CdHgTe epilayers grown on silicon substrates

We have studied the photoluminescence (PL) spectra of thin layers of mercury cadmium telluride (CdHgTe) solid solutions grown by molecular beam epitaxy on silicon substrates. It is established that a disorder in the solid solution structure in these layers does not exceed that in the layers grown by the same method on GaAs substrates. The PL spectra of CdHgTe/Si samples exhibit emission lines characteristic of the structurally perfect material, in particular, the lines due to donor-acceptor recombination and the recombination of excitons bound to impurities.