E. A. Grebenshchikova

A 2.78-μm laser diode based on hybrid AlGaAsSb/InAs/CdMgSe double heterostructure grown by molecular-beam epitaxy

A mid-IR laser based on a hybrid pseudomorphic AlGaAsSb/InAs/CdMgSe heterostructure with a III–V/II–VI heterovalent interface at the 0.6-μm-InAs active region has been fabricated by molecular-beam epitaxy on p+-InAs substrate. It provides ∼1.5-eV asymmetric barriers for both electrons and holes in InAs, inhibiting carrier leakage from the active region. Despite a nonoptimal defect density at the CdMgSe/InAs interface (106–107 cm−2), the structure demonstrates lasing at ∼2.78 μm (up to 100 K) under pulse injection pumping with the threshold current density of 3–4 kA/cm2. The proposed design is promising for high-power mid-IR lasers operating at room temperature.

Infrared whispering-gallery-mode lasers (λ= 2.4 μm) with convex disk cavity operating at room temperature

A whispering gallery mode (WGM) semiconductor laser with a convex disk cavity operating at room temperature in the middle-IR range (λ = 2.4 μm) has been created for the first time. The convex cavity was formed by etching in a specially selected CrO3-HF-H2O mixture. The room-temperature emission spectra have been measured. The laser generates WGMs at room temperature in a pulsed regime.

Broken-gap heterojunction in the p-GaSb-n-InAs1−x Sbx(0≤x≤0.18) system

Epitaxial InAs1−xSbx layers with the Sb content 0≤x≤0.18 were grown by metalorganic vapor phase epitaxy (MOVPE) on p-GaSb and n-InAs substrates. The photoluminescence (PL) spectra of the heterostructures were measured at T=77 K. The experimental PL data were used to study variation of the bandgap as a function of the InAsSb solid solution composition. The energy difference between the GaSb valence band top and the InAs0.82Sb0.18 conduction band bottom was calculated. It was established that GaSb/InAs1− xSbx with 0≤x≤0.18 represents a broken-gap heterojunction of type II.

Electrical properties of Pd-oxide-InP structures

Pd-anodic oxide-InP metal-oxide-semiconductor (MOS) structures are fabricated to develop a hydrogen sensor capable of effectively operating at room temperature. The conduction mechanisms of the structures at 100–300 K are studied. It is found that the oxide behaves as ohmic resistance and the rectifying properties of the structures are determined by the potential barrier at the oxide-InP interface with the thermal-tunneling charge transport mechanism. The structures greatly change their characteristics in the presence of hydrogen in the ambient medium.

LEDs (λmax = 3.6 μm) with cone-shaped light-emitting surfaces

A series of light-emitting diodes (LEDs) operating at λmax = 3.6 μm are created using cone-shaped mesas with heights of 10–130 μm and concave side surfaces. The dependence of the efficiency of room-temperature (T = 298 K) emission on the mesa height at various injection currents has been studied. The character of the observed dependence agrees with the results of theoretical calculations. The output radiation power of LEDs with the maximum mesa height (130 μm) at a pumping current of 220 mA amounts to 53 μW, which is 1.5 times higher than the power of LEDs with a mesa height of 10 μm.

Properties of GaSb-based LEDs with grid ohmic contacts

We studied light-emitting diodes (LEDs) based on GaSb-GaInAsSb-GaAlAsSb heterostructures with the emission due to electron transitions from the conduction band to levels of intrinsic double-charged acceptors. Parallelepiped-shaped LEDs with a round or gridlike contact on the surface of the epitaxial layer were studied experimentally and theoretically. The relations describing the current spreading from round and grid contacts are presented. It is shown that grid contacts, in contrast to round ones, provide a uniform distribution of current over the emitting layer. The current density under a grid contact is smaller than under a round one by a factor of 20, which is especially important for long-wavelength (λ≳2 µm) LEDs, in which the contribution of the nonradiative Auger recombination is significant. An emission power of 3.5 mW at 300 mA current is obtained from grid-contact LEDs.

InAs/InAsSbP light-emitting structures grown by gas-phase epitaxy

Using the metal-organic chemical vapor decomposition technique, light-emitting diodes based on InAs/InAsSbP double heterostructures emitting in a wavelength range around 3.3 µm have been fabricated. The external quantum yield of the diodes is 0.7%. In laser diodes, stimulated emission at a wavelength of 3.04 µm has been obtained at T=77 K.

Photodiodes based on InAs/InAsSb/InAsSbP heterostructures with quantum efficiency increased by changing directions of reflected light fluxes

It is shown, using the example of InAs/InAsSb/InAsSbP heterostructures, that the formation of a curvilinear reflecting surface consisting of hemispherical etch pits on the rear side of a photodiode chip leads to an increase in the quantum efficiency of photodiodes by a factor of 1.5–1.7 in the entire mid-IR wave-length interval studied (λ = 3–5 μm). For the obtained photodiodes with a cutoff wavelength of 4.8 μm, a photosensitive area of 0.1 mm2, and a chip area of 0.9 mm2, a monochromatic responsivity at λ = 4.0 μm reached 0.6 A/W, while a dark current at a reverse bias voltage of 0.2 V was within 4–6 A/cm2.

Interference of emission from disk-shaped lasers based on quantum-confined AlGaAsSb/InGaAsSb nanoheterostructures

Directivity patterns of disk-shaped whispering gallery mode (WGM) semiconductor lasers based on quantum-confined AlGaAsSb/InGaAsSb nanoheterostructures have been studied. The cavities of disk lasers were manufactured by wet chemical etching and had the shape of a truncated cone with a height of 15 μm. The top (about 5-μm-high) part of the cavity had a cylindrical shape. A flat ring with a width equal to the thickness of the active region was protruding ∼1 μm out of the side face of the cavity. The directivity diagram of the disc WGM laser exhibits a ring-shaped interference pattern with several maxima separated by an angle of ∼6°. The interference pattern observed in both spontaneous and laser generation regimes can be explained by the interference of rays emitted directly from the ring and those reflected from the etched surface of the crystal.

Enhancement of the spectral sensitivity of photodiodes for the mid-IR spectral range

A new method is used to raise the spectral sensitivity of photodiodes based on GaSb/GaInAsSb/GaAlAsSb heterostructures for the spectral range 1.1–2.4 μm. It is shown that, with a profile formed as pits on the metal-free unilluminated rear surface area of the photodiode chip, it is possible to improve the spectral sensitivity of the photodiodes at wavelengths in the range 1.8–2.4 μm. The most pronounced increase of up to 53% at the sensitivity maximum, compared with the sensitivity of conventional photodiodes with a fully metallized rear surface of the chip, is observed for photodiodes with shallow pits 30 μm in radius on their rear surface. These devices can find wide application in systems measuring the amount of water in petroleum products and the moisture content of paper, soil and grain.