Yu. P. Yakovlev

2.7–3.9 μm InAsSb(P)/InAsSbP low threshold diode lasers

Lasing has been obtained in the wavelength range 2.7–3.9 μm in double heterostructure diode lasers with an active region made of InAs alloys. The devices were grown by liquid‐phase epitaxy. Typical values of threshold current at 80 K were as low as 40 mA and the maximum operating temperature was 180 K. The blue shift of lasing modes was observed with current. This was explained by the increase of the carrier density in the active region above threshold due to intervalence band absorption.

InSb/InAs quantum dots grown by liquid phase epitaxy

The first original results on the growth of quantum dots (QDs) in the InSb/InAs system by liquid phase epitaxy (LPE) are reported. The density and dimensions of QDs were studied by methods of scanning probe microscopy and atomic force microscopy. The surface density, shapes, and dimensions of LPE-grown nanoislands depend on the growth conditions (temperature, cooling rate, and solution melt-substrate contact time). In the interval of temperatures T = 420–445°C, homogeneous arrays of InSb quantum dots on InAs(100) substrates were obtained with an average height of H = 3.4 ± 1nm, a radius of R = 27.2 ± 7.5 nm, and a density of up to 1.9 × 1010 cm−2.

Specific features of the epitaxial growth of narrow-gap InSb quantum dots on an InAs substrate

Arrays of coherent InSb quantum dots (QDs) have been fabricated by liquid-phase epitaxy on InAs substrates in the temperature range T = 420–450°C. The QDs with a density of (0.9−2) × 1010 cm−2 were 3 nm high and 13 nm in diameter. A bimodal QD size distribution was observed, which was accounted for by a combined growth mechanism of these nanoobjects. Structural characteristics of a separate InSb QD formed on the InAs surface were studied for the first time by atomic-force and transmission electron microscopies. Moire fringes were observed for the first time for QDs in the InSb/InAs system, with the moire period of 3.5 nm corresponding to InSb QDs without an admixture of arsenic.

Experimental observation of whispering gallery modes in sector disk lasers

The existence of the whispering gallery modes in a sector disk resonator has been demonstrated theoretically and experimentally observed in a disk, half-disk, and quarter-disk semiconductor lasers. The half-disk and quarter-disk lasers are fabricated from 285μm diameter disks emitted near 2.13μm at room temperature with continuous wave threshold currents of 55–60mA. Mode spacing in emission spectra of the half-disk lasers was the same as for the whole disk and doubled for the quarter disk as expected from the theoretical analysis. Half-disk lasers emit two parallel beams from the cleaved facet, while the two output beams are perpendicular in quarter-disk devices.

Light-emitting diodes based on GaSb alloys for the 1.6–4.4 μm mid-infrared spectral range

The available publications concerned with fabrication and study of light-emitting diodes (LEDs) intended for operation in the 1.6–4.4 μm spectral range; based on GaSb substrates; and grown by liquid-phase epitaxy, which makes it possible to form fairly thick layers lattice-matched to GaSb, are reviewed. In these studies, the active region consists of the GaInAsSb compound in LEDs for the spectral ranges 1.8–2.4 and 3.4–4.4 μm and the AlGaAsSb compound for the spectral region 1.6–1.8 μm. The wide-gap AlGaAsSb confining layers contain up to 64% of Al, which is an unprecedentedly high content for liquid-phase epitaxy. Asymmetric (GaSb/GaInAsSb/AlGaAsSb) and symmetric (AlGaAsSb/GaInAsSb/AlGaAsSb) heterostructures have been fabricated and studied. Various types of designs that make it possible to improve the yield of radiation generated in the active region have been developed. The measured external quantum yield of emission is as high as 6.0% at 300 K for the LEDs operating at the wavelengths 1.9–2.2 μm. A pulsed optical-radiation power of 7 mW at a current of 300 mA with a duty factor of 0.5 and 190 mW at a current of 1.4 A with a duty factor of 0.005 have been obtained. The external quantum emission yield of ∼1% has been obtained for LEDs that emit in the spectral range 3.4–4.4 μm; this yield exceeds that obtained for the known InAsSb/InAsSbP heterostructure grown on an InAs substrate by a factor of 3. The measured lifetime of minority charge carriers (5–0 ns) is close to the theoretical lifetime if only the radiative recombination and impact CHCC bulk recombination are taken into account. The impact recombination is prevalent at temperatures higher than 200 K for LEDs operating in the spectral range 3.4–4.4 μm and at temperatures higher than 300 K for LEDs operating in the spectral range 1.6–2.4 μm.

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.

Room-temperature midinfrared electroluminescence from asymmetric AlSbAs/InAs/CdMgSe heterostructures grown by molecular beam epitaxy

A hybrid double heterostructure with large asymmetric band offsets, combining AlAsSb/InAs (as a III–V part) and CdMgSe/CdSe (as a II–VI part), has been proposed as a basic element of a midinfrared laser structure design. The p-i-n diode structure has been successfully grown by molecular beam epitaxy and has exhibited an intense long-wavelength electroluminescence at 3.12 μm (300 K). A less than 10 times reduction of electroluminescence intensity from 77 to 300 K indicates an efficient carrier confinement in the InAs active layer due to high potential barriers in conduction and valence bands, estimated as ΔEC=1.28 eV and ΔEV∼1.6 eV. The type of band lineups at a coherent InAs/Cd1−xMgxSe interface is discussed for 0⩽x⩽0.15.

Interface electroluminescence of confined carriers in type II broken-gap p-GaInAsSbp-InAs single heterojunction

Abstract A first observation of electroluminescence in type II broken-gap isotype p- GaInAsSb p- InAs single heterojunction is reported. Two narrow luminescence peaks were observed in the spectral range of λ = 3–4 μm at T = 77K with full width at half maximum (FWHM) about 10–20 meV. Spectral position and intensity of these emission bands can be changed by drive current, and “blue” shift was observed with increasing current. Intensive spontaneous emission was obtained up to room temperature. It was found that unusual electroluminescence is due to indirect (tunnel) radiative recombination of spatially separated electrons and holes localized in deep adjacent quantum wells at the different sides of the interface. A new physical approach for the design of mid-infrared lasers using a type II broken-gap p-p heterojunction as an active layer is proposed.

Physical working principles of semiconductor disk lasers

The physical working principles of whispering gallery mode semiconductor disk lasers are examined. A new method is proposed for measuring the single-pass gain. The theory of cylindrical waveguides is considered. The spectral characteristics of whispering gallery mode lasers is investigated experimentally in the temperature range 4-300 K. It is shown that lasers of this kind are very promising as potential laser radiation sources operating at room temperature.

Current-tunable lasers with a narrow emission line operating at 3.3 µm

Current-tunable diode lasers with narrow emission lines for laser spectroscopy in the 3.2–3.4 µm wavelength range are developed. The lasers, based on an InAsSb/InAsSbP double heterostructure, have a wide-stripe cavity. The wave number increases from 3030 to 3034 cm−1 as the current is raised from 1.5 to 3 times the threshold value at 70 K, while the full width at half-maximum of the laser line decreases from 18 to 10 MHz. It is demonstrated that the linewidth is determined by fluctuations of the cavity resonance frequencies as a result of fluctuations in the concentration of nonequilibrium charge carriers.