Calibration of the spectral sensitivity of instruments for the near infrared region

We present an analysis of methods for calibration of the spectral sensitivity of instruments in the near IR region of the spectrum (0.90–2.05 μm), using as an example recording of the luminescence spectra of PbS semiconductor quantum dots using a diffraction monochromator and an InGaAs photodiode as the detector. We show that when high-sensitivity detectors are employed for calibration using the emission spectrum of an ideal black body, the problem of attenuation of the radiation flux is still important. Instead of neutral density glass and mesh light filters for attenuation of the radiation, we propose using UFS ultraviolet optical glasses (together with PS purple glasses), the maximum optical density of which is within the region of maximum spectral sensitivity of InGaAs photodiodes. We give examples of spectral calibration, taking into account instrumental characteristics and the effect of absorption by water vapor in the air, and also corrections of the luminescence spectra of quantum dots.     

Physical Analysis of a Possibility to Reach the 1.30-μm Emission from the GaAs-Based VCSELs with the InGaAs/GaAs Quantum-Well Active Regions and the Intentionally Detuned Optical Cavities

Physical aspects of an operation of the GaAs-based InGaAs/GaAs quantum-well (QW) VCSELs with the intentionally detuned optical cavities have been considered in the present paper using the comprehensive three-dimensional self-consistent optical–electrical–thermal-gain simulation. In GaAs-based structures, very good DBR resonator mirrors and a very efficient methods to confine radially both the current spreading and the electromagnetic field with the aid of oxide apertures may be applied. It has been found using the above simulation that even currently available immature technology enables manufacturing the above devices emitting radiation of wavelengths over 1.20 μm. In particular, while the room-temperature 1.30-μm lasing emission is still beyond possibilities of the InGaAs/GaAs QW VCSELs, these structures may offer analogous 1.25-μm emission, especially for the high-power and/or high-temperature operation.     

Quantum structures for multiband photon detection

The work describes multiband photon detectors based on semiconductor micro-and nano-structures. The devices considered include quantum dot, homojunction, and heterojunction structures. In the quantum dot structures, transitions are from one state to another, while free carrier absorption and internal photoemission play the dominant role in homo or heterojunction detectors. Quantum dots-in-a-well (DWELL) detectors can tailor the response wavelength by varying the size of the well. A tunnelling quantum dot infrared photodetector (T-QDIP) could operate at room temperature by blocking the dark current except in the case of resonance. Photoexcited carriers are selectively collected from InGaAs quantum dots by resonant tunnelling, while the dark current is blocked by AlGaAs/InGaAs tunnelling barriers placed in the structure. A two-colour infrared detector with photoresponse peaks at ∼6 and ∼17 μm at room temperature will be discussed. A homojunction or heterojunction interfacial workfunction internal photoemission (HIWIP or HEIWIP) infrared detector, formed by a doped emitter layer, and an intrinsic layer acting as the barrier followed by another highly doped contact layer, can detect near infrared (NIR) photons due to interband transitions and mid/far infrared (MIR/FIR) radiation due to intraband transitions. The threshold wavelength of the interband response depends on the band gap of the barrier material, and the MIR/FIR response due to intraband transitions can be tailored by adjusting the band offset between the emitter and the barrier. GaAs/AlGaAs will provide NIR and MIR/FIR dual band response, and with GaN/AlGaN structures the detection capability can be extended into the ultraviolet region. These detectors are useful in numerous applications such as environmental monitoring, medical diagnosis, battlefield-imaging, space astronomy applications, mine detection, and remote-sensing. The paper presented there appears in Infrared Photoelectronics, edited by Antoni Rogalski, Eustace L. Dereniak, Fiodor F. Sizov, Proc. SPIE Vol. 5957, 59570W (2005).     

Far-IR radiation of hot holes in germanium for mutually perpendicular directions of uniaxial pressure and electric field

The advantages of crossed directions of an electric field and uniaxial pressure over a parallel configuration for obtaining lasing (λ≅100 μm) in p-type germanium are substantiated. The results of the first experiments investigating far-IR emission for mutually perpendicular directions of the field and pressure are reported. The pressure dependences of the radiation intensity in various electric fields are explained by the different hole occupation of the states of an impurity center which are split by uniaxial pressure. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 257–261 (25 August 1999)     

Efficient photoluminescence from triangular quantum wells at the interface of an InP/In0.53Ga0.47As heterostructure

Efficient photoluminescence (PL) with quantum yield close to 1 from InP/In_0.53Ga_0.47As heterostructures (HSs) at temperatures 77–300 K and low excitation levels is observed and investigated. The PL is due to a quasi-triangular quantum well (TQW) located at the HS interface and consists of two spectrally similar lines: InGaAs interband emission and emission from the bottom level of the TQW. It is found that as the temperature increases, the intersubband emission rises, while the TQW radiation is quenched. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 783–787 (25 May 1998)     

A review on quantum well structures in photonic devices for enhanced speed and span of the transmission network

Quantum well devices feature heterostructures of very thin epitaxial layers of group III-V and II-VI semiconductor materials. Quantum well devices are integrated monolithically with various optoelectronics devices to provide photonic integrated circuits. The representative structure could be realized with GaAs wells with GaAlAs barriers for wavelengths around 0.9 μm and InGaAsP are used for longer wavelengths. Together with quantum well, superlattice structure is another popular design for InGaAs Avalanche Photo Diode (APD). Quantum well structures find their applications in improved lasers, superlattice for photodiodes, modulators and switches. Consequences of quantum well theory are available today in terms of quantum wires and quantum dots. Upon the application of the normal electric field to quantum well structures, exciton pairs becomes more and more confined and the sharp exciton absorption peaks are observed. The effect is termed as “Quantum Confined Stark Effect”. The electro-absorption effect is approximately 50 times larger in multiple quantum well structures than it is in bulk semiconductors. Another electro-absorption effect known as “Franz Keldysh Effect” has been employed in monolithic waveguide detector. These effects lead to electro-absorption lasers (EAL) as well as electro-absorption laser modulators (EML).     

On the passive probing of fiber optic quantum communication channels

Avalanche photodetectors based on InGaAs:P are the most sensitive and only detectors operating in the telecommunication wavelength range 1.30–1.55 μm in the fiber optic quantum cryptography systems that can operate in the single photon count mode. In contrast to the widely used silicon photodetectors for wavelengths up to 1 μm operating in a waiting mode, these detectors always operate in a gated mode. The production of an electron-hole pair in the process of the absorption of a photon and the subsequent appearance of an avalanche of carriers can be accompanied by the inverse processes of the recombination and emission of photons. Such a backward emission can present a potential serious problem for the stability of fiber optic quantum cryptography systems against passive probing. The results of analyzing the detection of backscattered radiation are reported. The probability of such an emission has been estimated.     

Electrical and electroluminescent properties of InAsSb-Based LEDs (λ = 3.85–3.95 μm) in the temperature interval 20–200°C

The temperature dependences of the electrical and electroluminescent properties of InAsSbP/InAsSb/InAsSbP heterostructure LEDs (λ ≈ 3.8−4.0 μm) are studied in the temperature interval 20–200°C. It is shown that the radiation power decreases with increasing temperature in a superexponential manner and that this decrease is associated primarily with a rise in the rate of Auger recombination. The position of the maximum in the radiation spectrum varies with temperature nonmonotonically, since radiative recombination is observed both in the active region and in the wide-gap layer. At room temperature, current through the heterostructure is tunneling current irrespective of the applied voltage polarity. As the temperature rises, either the thermal emission of charge carriers appears (direct bias) or the diffusion current becomes significant (reverse bias).     

Squeezed states of long-lived terahertz vibrations in quantum dots

Quantum dots based on materials with long-lived terahertz vibrations are studied. It is shown that squeezed states of such vibrations can result in microwave-frequency modulation of the optical radiation absorbed at electronic transitions in quantum dots. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 2, 199–200 (25 January 1997)     

Electron-beam-pumped infrared and visible lasers

This paper presents the results of investigations of lasing by electronic transitions of xenon, krypton, and neon atoms, cadmium and zinc ions, and nitrogen molecules and by oscillatory transitions of HF molecules. The processes responsible for the efficiency of each of the lasers have been studied. The maximum radiation energies achieved are as follows: up to 200 J at λ∼2.8 μm for a mixture of H₂−SF₆, up to 100 J at λ-1.73 μm and up to 50 J at λ=2.03 μm for xenon, up to 3 J at λ=358 nm for a mixture of Ar−N₂, and up to 0.5 J at λ=585.5 nm for neon. Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 34–44, April, 2000.     

Raman scattering of light by optical phonons in Si-Ge-Si structures with quantum dots

Raman scattering of light by optical phonons in Si-Ge-Si structures with pseudomorphic germanium quantum dots has been investigated. Resonance amplification of the scattering intensity on E ₀ (Γ₇−Γ₈) transitions has been observed. It is shown that as a result of the formation of the layer of germanium quantum dots, the resonance energy is ∼0.3 eV higher than in the two-dimensional case. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 203–207 (10 August 1996)     

Mid infrared interband cascade lasers for sensing applications

The growth of Interband Cascade Laser material to cover the wavelength range from 3–4 μm is presented along with the fabrication and characterization of Broad Area (BA) and Ridge Waveguide (RWG) devices based on this material. Pulsed operation slightly below room temperature is observed for both device types, and a strong reduction of threshold currents can be observed in the RWG lasers. Variation of the active Quantum Well width in the epitaxial structures enables laser emission in the 3–4 μm wavelength region.     

Photoinduced improvement of the properties of light-emitting diodes

Results from studies of the effect of the action of optical radiation on the characteristics of light-emitting diodes (LEDs) produced using the binary heterostructure Ga_xAl_1−xAs (λ=0.88 μm) are presented. High sensitivity of the LED to the following parameters of the optical radiation is shown: flux density, quantum energy, and exposure dose. The action of optical radiation in the form of a band with a maximum at 255 nm on the LED heterostructures lowers the leakage current into the bulk, decreases the loss identified as surface leakage current by about an order of magnitude, increases the radiated power by 50–100% in the current region up to 10⁻³ A, and increases the overall light output of the diodes. Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 109–114, August, 1997.     

Comparison of single-layer and bilayer InAs/GaAs quantum dots with a higher InAs coverage

Epitaxially grown self-assembled InAs quantum dots (QDs) have found applications in optoelectronics. Efforts are being made to obtain efficient quantum-dot lasers operating at longer telecommunication wavelengths, specifically 1.3 μm and 1.55 μm. This requires narrow emission linewidth from the quantum dots at these wavelengths. In InAs/GaAs single layer quantum dot (SQD) structure, higher InAs monolayer coverage for the QDs gives rise to larger dots emitting at longer wavelengths but results in inhomogeneous dot-size distribution. The bilayer quantum dot (BQD) can be used as an alternative to SQDs, which can emit at longer wavelengths (1.229 μm at 8 K) with significantly narrow linewidth (∼16.7 meV). Here, we compare the properties of single layer and bilayer quantum dots grown with higher InAs monolayer coverage. In the BQD structure, only the top QD layer is covered with increased (3.2 ML) InAs monolayer coverage. The emission line width of our BQD sample is found to be insensitive towards post growth treatments.     

Characteristic features of the x-ray spectra of a plasma produced by heating CO2 clusters by intense femtosecond laser pulses with λ=0.8 and 0.4 μm

The x-ray spectra of a plasma produced by heating CO₂ clusters with intense femtosecond laser pulses with λ=0.8 μm and λ=0.4 μm are investigated. Spatially resolved x-ray spectra of the cluster plasma are obtained. The observed characteristic features of the x-ray emission spectra show unequivocally that such a plasma contains quite a large relative number of ions (≃10⁻²–10⁻³) with energies of 0.1–1 MeV. The contour of the OVIII Ly_α line is found to have characteristic features that are especially conspicuous when the clusters are heated with second-harmonic pulses. These features cannot be explained by any mechanisms known to the authors. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 454–459 (25 September 1998)     

Mechanism of field emission from carbon materials

Field emission in diamond and graphite-like polycrystalline films is investigated experimentally. It is shown that the emission efficiency increases as the nondiamond carbon phase increases; for graphite-like films the threshold electric field is less than 1.5 V/μm, and at 4 V/μm the emission current reaches 1 mA/cm², while the density of emission centers exceeds 10⁶ cm⁻². A general mechanism explaining the phenomenon of electron field emission from materials containing graphite-like carbon is proposed. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 56–60 (10 July 1998)     

High-quality MBE growth of AlχGa1-χ As-based THz quantum cascade lasers

High-quality GaAs-based quantum cascade laser (QCL) structures for the terahertz (THz) emission have been grown by solid source molecular-beam epitaxy. Ex-situ high-resolution x-ray diffraction shows that layer thickness and its control is the most critical growth aspect and that the lasing potential of the structure can be determined by the thickness accuracy of the layers. For our samples, the thickness tolerance for working lasing structures emitting approximately 100 μm was determined to be minimally above 1% for a 15 μm active region which was composed of 54.6 nm cascade cells. Increasing interface roughness adversely affects the lasing threshold and power. Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia     

Photoluminescence of InAs quantum dots embedded in graded InGaAs barriers

The effects of the top barrier and the dot density on photoluminescence (PL) of the InAs quantum dots (QDs) sandwiched by the graded In_xGa_1−xAs barriers grown by metal-organic vapor phase epitaxy (MOVPE) have been studied. Two emission peaks corresponding to the ground state and the 1st excited state transitions of the QD structures have been observed, which matches well to the theoretical calculation. The PL emission linewidth and intensity of the InAs QDs structure are improved by reducing the Indium/Gallium composition variation of the graded In_xGa_1−xAs top barrier layer of the structure. The QDs’ ground states filling excitation power depends on the crystal quality of the InGaAs barrier layer and the QD density. The extracted thermal activation energy for the QDs’ PL emission is sensitive to the QD size.     

Band structures and characteristics of InGaAs/InGaAsP strain-compensated quantum well lasers

Analysis is performed for valence band structures and some characteristics of InGaAs/InGaAsP strain-compensated quantum well lasers lattice-matched to InP substrate. The computed results show that band offsets are functions of strain compensation instead of constants; strain compensation changes the band structures and the density of states, and hence affects the optical gain and the threshold current density. Under the condition of zero net strain, the values of the well width, cavity length and relative threshold carrier density and threshold current density are determined for realization of 1.55 m wavelength emission.     

Corrugated neat thin-film conjugated polymer distributed-feedback lasers

Wave-guided thin-film distributed-feedback (DFB) polymer lasers are fabricated by spin coating a PPV-derived semiconducting polymer, thianthrene-DOO-PPV, onto oxidised silicon wafers with corrugated second-order periodic gratings. The gratings are written by reactive ion beam etching. Laser action is achieved by transverse pumping with picosecond laser pulses (wavelength 347.15 nm, duration 35 ps). The DFB-laser surface emission and edge emission are analysed. Outside the grating region the polymer film is used for comparative wave-guided travelling wave laser (amplified spontaneous emission (ASE)) studies. The pump pulse threshold energy density for wave-guided DFB-laser action (4–9 μJ cm^-2) is found to be approximately a factor of two lower than the threshold for wave-guided travelling wave laser action. The spectral width of the DFB laser (down to Δλ_DFB≈0.07 nm) is considerably narrower than that of the travelling wave laser (Δλ_TWL≈14 nm). The DFB-laser emission is highly linearly polarised transverse to the grating axis (TE mode). Only at high pump pulse energy densities does an additional weak TM mode build up. The surface-emitted DFB-laser radiation has a low divergence along the grating direction. For both the DFB lasers and the travelling wave lasers, gain saturation occurs at high excitation energy densities. Received: 7 January 2002 / Revised version: 15 February 2002 / Published online: 14 March 2002