High peak power 16 μm InP-related quantum cascade laser

In this paper ～16 μm-emitting multimode InP-related quantum cascade lasers are presented with the maximum operating temperature 373 K, peak and average optical power equal to 720 mW and 4.8 mW at 303 K, respectively, and the characteristic temperature (T₀) 272 K. Two types of the lasers were fabricated and characterized: the lasers with a SiO₂ layer left untouched in the area of the metal-free window on top of the ridge, and the lasers with the SiO₂ layer removed from the metal-free window area. Dual-wavelength operation was obtained, at λ ～ 15.6 μm (641 cm^?1) and at λ ～ 16.6 μm (602 cm^?1) for lasers with SiO₂ removed, while within the emission spectrum of the lasers with SiO₂ left untouched only the former lasing peak was present. The parameters of these devices like threshold current, optical power and emission wavelength are compared. Lasers without the SiO₂ layer showed ～15% lower threshold current than these ones with the SiO₂ layer. The optical powers for lasers without SiO₂ layer were almost twice higher than for the lasers with the SiO₂ layer on the top of the ridge.     

Modeling and experimental study of 780–808-nm AlGaAs/GaAs injection lasers with electron superlattice barriers

Electron superlattice barriers (ESBs) were used in AlGaAs/GaAs injection lasers to improve the electron confinement of the active layer by Bragg reflection of electron waves. The design of a separate-confinement heterostructure (SCH) laser with ESBs operating at 780–808 nm was optimized. Conventional SCH and SCH-ESB were prepared by low-pressure MOCVD epitaxy. Oxide stripe lasers with stripe widths of 100 and 200µm were prepared. The threshold current density of 0.3 kA/cm² and the characteristic temperature constantT ₀=220 K were measured at a wavelength of 808 nm for SCH-ESB lasers with an active-layer thickness of 40 nm and a resonator length of 0.4–0.5 mm. For conventional SCH lasers with the same geometry, a threshold current density of 0.42 kA/cm² andT ₀=160 K were obtained. Experimental results on the low-temperature photoluminescence characterizing ESB regions are presented and are compared with the calculated miniband energy spectrum of the superlattice structure. The leakage currents for ordinary SCH and SCH-ESB lasers were analyzed. Experimental verification of a reduction in the leakage current for SCH-ESB lasers was obtained.     

Type III - Type I transition and strain-effect in Hg1−xCdxTeCdTe and Hg1−xZnxTeCdTe superlattices

In this paper, the results of Hg_1−xZn_xTeCdTe strained layer superlattices grown by MBE are reported, and compared to Hg_1−xCd_xTeCdTe superlattices. Both Type III and Type I Hg_1−xZn_xTeCdTe superlattices with different strain have been grown on CdTe(111)B/GaAs(100) and CdTe(100)/GaAs(100) substrates and characterized by electron, X-ray diffraction, infrared transmission and Hall measurements. The values of hole mobility between 5×10³ up to 2×10⁴cm²v⁻¹s⁻¹ at T = 23K along (111)B growth orientation and up to 4.9×10⁴cm²v⁻¹s⁻¹ at T = 5K along (100) growth orientation are obtained for Type III superlattices whereas in Type I superlattices, the hole mobility is between 200–300cm²v⁻¹s⁻¹. This drastic change in the hole mobility between Type III and Type I superlattices along with the role of the strain are discussed in this paper.     

Polarized reflectance spectrum of β-(BEDT-TTF)2PF6

The polarized reflectance spectrum of β-(BEDT-TTF)₂PF₆ was measured over the spectral range from 720 cm^?1 to 25, 000 cm^?1 at 293 K (semiconductive phase) and at 318 K (metallic phase). The infrared band found in the conductivity spectrum, which was obtained by the Kramers-Kronig transformation of the reflectance data, is interpreted as the one associated with inter-band transition.     

Infrared diode laser spectroscopy

Three types of lasers (double-heterostructure 66 K InAsSb/InAsSbP laser diode, room temperature, multi quantum wells with distributed feedback (MQW with DFB) (GaInAsSb/AlGaAsSb based) diode laser and vertical cavity surface emitting lasers (VCSELs) (GaSb based) have been characterized using Fourier transform emission spectroscopy and compared. The photoacoustic technique was employed to determine the detection limit of formaldehyde (less than 1 ppmV) for the strongest absorption line of the v₃ + v₅ band in the emission region of the GaInAsSb/AlGaAsSb diode laser. The detection limit (less than 10 ppbV) of formaldehyde was achieved in the 2820 cm⁻¹ spectral range in case of InAsSb/InAsSbP laser (fundamental bands of v₁, v₅). Laser sensitive detection (laser absorption together with high resolution Fourier transform infrared technique including direct laser linewidth measurement, infrared photoacoustic detection of neutral molecules (methane, form-aldehyde) is discussed.     

Measurements of near-IR water vapor absorption at high pressure and temperature

Tunable diode lasers (TDLs) are used to measure high resolution (0.1 cm^-1), near-infrared (NIR) water vapor absorption spectra at 700 K and pressures up to 30 atm within a high-pressure and -temperature optical cell in a high-uniformity tube furnace. Both direct absorption and wavelength modulation with second harmonic detection (WMS-2f) spectra are obtained for 6 cm^-1 regions near 7204 cm^-1 and 7435 cm^-1. Direct absorption measurements at 700 K and 10 atm are compared with simulations using spectral parameters from HITRAN and a hybrid database combining HITRAN with measured spectral constants for transitions in the two target spectral regions. The hybrid database reduces RMS error between the simulation and the measurements by 45% for the 7204 cm^-1 region and 28% for the 7435 cm^-1 region. At pressures above 10 atm, the breakdown of the impact approximation inherent to the Lorentzian line shape model becomes apparent in the direct absorption spectra, and measured results are in agreement with model results and trends at elevated temperatures reported in the literature. The wavelength-modulation spectra are shown to be less affected by the breakdown of the impact approximation and measurements agree well with the hybrid database predictions to higher pressures (30 atm). PACS 33.20.Ea; 42.62.Fi; 52.25.Os     

Experimental low energy values of CH4 transitions near 1.33 μm by absorption spectroscopy at 81 K

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by direct absorption spectroscopy between 1.36 and 1.30 μm (7351-7655 cm⁻¹) using a cryogenic cell and a series of distributed feed back (DFB) diode lasers. The investigated spectral range corresponds to the high energy part of the icosad dominated by the ν₂+2ν₃ band near 7510 cm⁻¹. The positions and strengths at 81 K of 3473 transitions were obtained from the spectrum analysis. The minimum value of the measured line intensities (at 81 K) is on the order of 10⁻²⁶ cm/molecule, i.e. significantly lower than the intensity cut off of the HITRAN database in the region (4×10⁻²⁵ cm/molecule at 296 K). From the variation of the line strength between 81 and 296 K, the low energy values of 1273 transitions could be determined. They represent 69% and 81% of the absorbance in the region at 296 and 81 K, respectively. The obtained results are discussed in relation with the few rovibrational assignments previously reported in the region.     

Light hole transport in a strained GaAs/In0.18Ga0.82As quantum well at high pressures

Abstract

Here we report what we believe to be the first observation of the pressure dependence of the light hole behavior in a modulation doped In_0.18Ga_0.82As/GaAs single strained quantum well grown by MBE. Transport measurements have been undertaken as a function of temperature (4–300K) and hydrostatic pressure (4–8kbar). Hole mobilities of ～17000 cm²/Vs have been obtained for sheet carrier densities of ～3.3×10¹¹ cm^?2. At low temperatures (<100K) persistent photogenerated holes have been observed. The hole mobility is found to decrease with increasing pressure at a rate intermediate between that typically observed for holes and electrons in bulk III-V semiconductors.     

Temperature and injection current dependent electroluminescence study of GaInP/AlGaInP quantum well laser diode grown using tertiarybutylarsine and tertiarybutylphosphine

GaInP/AlGaInP triple quantum well (TQW) lasers, grown by metalorganic chemical vapor deposition (MOCVD) using tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP), were fabricated with a pulsed anodic oxidation (PAO) process. The devices worked at room temperature (RT) with the lowest threshold current density (J_th) of 1.5 kA/cm² ever reported for GaInP/AlGaInP lasers grown using TBAs and TBP. Temperature dependent (35–250 K) electroluminescence (EL) study of the GaInP/AlGaInP laser diode showed almost the same luminescence quenching behavior at a high temperature region (120–250 K), independent of the injection current (100–150 mA). A model involving a nonradiative recombination mechanism was presented to interpret the EL quenching behavior over the experimental temperature range. The nonradiative recombination centers in the Al-containing barrier or cladding layer are believed to contribute to the loss of carriers via nonradiative recombination. PACS 78.60.Fi; 71.20.Nr; 78.67.De; 81.15.Gh; 42.55.Px     

Temperature dependence of the absorption spectrum of CH4 by high resolution spectroscopy at 81 K: (II) The icosad region (1.49-1.30 μm)

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by differential absorption spectroscopy between 6717 and 7351 cm⁻¹ (1.49-1.36 μm) using a cryogenic cell and a series of distributed feed back (DFB) diode lasers. The investigated spectral region corresponds to the very congested low energy part of the icosad for which the HITRAN database provides neither rovibrational assignments nor the lower state energies. The positions and strengths at 81 K of 9389 transitions were obtained from the spectrum analysis. The minimum value of the measured line intensities (at 81 K) is on the order of 10⁻²⁶ cm/molecule. From the variation of the line strength between 81 K and 296 K, the low energy values of a total of 4646 transitions were determined. They represent 79.4% and 68.4% of the total absorbance in the region at 81 and 296 K, respectively, and include 28 transitions assigned to the ν₂+4ν₄ band near 6765 cm⁻¹. The reliability of the method based on the association of lines with coinciding centers in the 81 K and 296 K spectra is discussed. The results of the present analysis have been combined with previously analyzed high energy part of the icosad dominated by the ν₂+2ν₃ band near 7510 cm⁻¹. The line list for the whole icosad (6717-7655 cm⁻¹) consists of 12 865 transitions at 81 K.     

Mobility enhancement in MBE-grown InxGa1−xAs/In0.52Al0.48As modulation-doped heterostructures

Pseudomorphic In_xGa_1−xAs/In_0.52Al_0.48As modulation-doped heterostructures were grown by molecular beam epitaxy (MBE) on InP (100) substrates over a range of indium compositions fromx=0.53 to 0.75. Low temperature photoluminescence (PL) measurements show a prominent reduction in the InGaAs linewidth due to the quantum-size effect as the indium composition is increased from its lattice-matched value of 0.53. The lowest linewidth of 6.8 meV was achieved at an indium composition of 0.65, above which an increase in the linewidth was observed due to the overwhelming effects of interfacial strain. The Hall mobilities at 300 K and 77 K increase in correspondence to the PL linewidth reduction as the indium composition is increased. Although initial signs of mobility saturation can be seen at an indium composition of 0.65, the peak mobility at 77 K of 8.9×10⁴cm²V s⁻¹was achieved at an indium composition of 0.70. There is experimental evidence to indicate that the mobility enhancement at increasing indium composition is due to an effect of a reduction in the alloy scattering and in the effective mass of the carriers. It was found that the insertion of an additional In_0.53Ga_0.47As interface smoothing layer between the strained InGaAs channel and the In_0.52Al_0.48As spacer layer did not have a significant effect on the mobility enhancement in the heterostructures.     

HgCdTe buried multi-junction photodiodes fabricated by the liquid phase epitaxy

This article reports the parameters and characteristics of the new type of HgCdTe buried photodiodes operated at near-room temperature (T=200–300 K) in long wavelength infrared spectral range. The liquid phase epitaxy (LPE) Hg_1−xCd_xTe (x=0.16–0.20) layers were grown on holes etched in (1 0 0) CdZnTe substrate. Prior to layer deposition, the CdZnTe substrate has been etched to form the bars on 30 μm centers and 20-μm depth. Next, 20-μm thick HgCdTe epitaxial layer has been grown from Te-rich solution. The type of conductivity was controlled by deliberately doping with indium (n-type) and Sb (p-type). The Nomarski microscopy showed that the surface of specially prepared layers was flat and the composition of layers, measured by Fourier transform infrared microscopy, was homogenous. Samples were cleaved and examined in cross section by scanning electron microscopy. Finally, serial connected multi-junction photodiodes have been fabricated. It is shown that LPE can be used to realise advanced bandgap engineered multi-junction structures. This conclusion is supported by device quality characteristics: spectral response and detectivity.     

Very narrow-bandwidth tunable infrared difference frequency generation with injection-locked dye lasers

Two flashlamp pumped dye lasers of very high spectral quality are mixed in a LiIO₃ crystal to generate a tunable infrared beam through the difference frequency mixing. Thanks to the injection-locking process of the pulsed dye lasers leading to a linewidth of 6 MHz with peak powers of about 10 kW, we obtain an IR beam tunable from 3.5 to 5.9 m with a peak power of 40 W and a linewidth of 9 MHz. As an application we present a spectrum of N₂O obtained by differential absorption near 1880 cm^–1. The lines of thisQ-branch are Doppler limited at the working pressure (10² Pa).     

A novel method for positioning of InAs islands on GaAs (1 1 0)

A novel method for positioning of InAs islands on GaAs (1 1 0) by cleaved edge overgrowth is reported. The first growth sample contains strained In_xGa_1−xAs/GaAs superlattice (SL) of varying indium fraction, which acts as a strain nanopattern for the cleaved-edge overgrowth. Atoms incident on the cleaved edge will preferentially migrate to InGaAs regions where favorable bonding sites are available. By this method InAs island chains with lateral periodicity defined by the thickness of InGaAs and GaAs of SL have been realized by molecular beam epitaxy (MBE). They are observed by means of atomic force microscopy (AFM). The strain nanopattern's effect is studied by the different indium fraction of SL and MBE growth conditions.     

单边分子束外延硅pn结C-V关系的新特点

本文研究了以分子束外延硅为超薄n区的pn结的C-V特性,推导了当该结的耗尽区扩展到外延层边缘后的C^-2-V关系。据此,由实验可求出非故意掺杂的硅分子束外延层的杂质浓度为8.0×10¹⁴cm^-3。从而建立起一种测量超薄分子束外延层掺杂浓度的新方法。 关键词：     

FIR and millimetric measurements from a pulsed emission

Frequency mixing of two pulsed CO₂ lasers in a AsGa crystal induces a very low frequency emission (between 40 and 4 cm^–1).Using these emissions for spectroscopic measurements is very interesting, due to the spectral range covered in this way. However the shortness of the pulses does not allow the transposition of the classical method used with continuous emitting pumped lasers.In this paper are studied different experimental methods used to obtain absorption measurements of a given substance, with the best possible accuracy.     

Thermal effects in quantum cascade lasers at λ～4.6 μm under pulsed and continuous-wave modes

The thermal effects in InGaAs/InAlAs quantum cascade lasers (QCLs) emitting at λ∼4.6 μm under pulsed and continuous-wave (CW) modes using a three-dimensional (3D) heat dissipation model were investigated. Based on the experimentally measured results, the thermal characteristics were theoretically analyzed for various device and heatsinking structures. Also, the heat accumulation effects and dissipation processes were studied in detail under pulsed operation. High cooling efficiencies were achieved by a relatively fast heat diffusion rate from the active core region for the epilayer-down bonded single ridge waveguide buried heterostructure (BH) with a thick electroplated Au around the laser ridge. A further improvement was made by the use of InP embedding layer. In CW mode, the thermal conductance (G _th) value of 445 W/(K cm²) at 298 K was obtained for the epilayer-down bonded double-channel ridge waveguide QCL with AlN submount, which indicates a reasonable consistency with the available experimental data. By optimizing the device and heatsinking structures, the G _th was improved to a high value of 673 W/(K cm²) at 298 K for the epilayer-down bonded single ridge waveguide BH QCL with InP embedding layer on diamond submount in CW mode.     

Laser-assisted etching of diamonds in air and in liquid media

2 O, (CH₃)₂SO). Diamond samples are virtually transparent at this wavelength, and the coupling of laser radiation to diamond is via the formation of a thin graphitized layer at the diamond surface. The etching rate in liquid media is slightly higher than in air at otherwise equal conditions and is as high as 50 μm/s for etching with a scanning laser beam. Raman spectra measurements carried out on diamond samples etched in air show the presence of glassy carbon on the surface, whereas for samples etched in a liquid the diamond peak at 1332 cm^-1 dominates with significantly lower intensity of the glassy carbon peak. Electroless copper deposition on the laser-etched features is studied to compare the catalytic activity of the diamond surface etched in air with that etched in liquids. Possible mechanisms responsible for the observed difference both in the structure of the etched area and in the electroless Cu deposition onto the surface etched in various media (air or liquids) are discussed. Received: 2 August 1996/Accepted: 7 January 1997     

Fourier Transform Mid-Infrared Photoacoustic Spectroscopy for Presymptomatic Detection of Powdery Mildew Infection in Rubus corchorifolius L.

A powdery mildew fungi-induced disease appearing on leaves of Rubus corchorifolius L. has been observed in China, which resulted in seriously influencing the yield and quality of the fruit, and a presymptomatic detection of powdery mildew infection is needed to guarantee the yield and quality through removing the fungi in an early stage. Depth-profiling Fourier transform mid-infrared photoacoustic spectroscopy was applied to characterize both the healthy leaves and powdery mildew-infected leaves of Rubus corchorifolius L. The profiled surface could be divided into out layer (depth of about 1.32 µm) and deep layer (depth of about 1.87 µm). There were numerous differences in the total spectral range (500–4000 cm^?1) between healthy leaves and infected leaves, especially the intensity of absorption bands of 2800–3000 cm^?1 (aliphatic C–H vibration) and 2250–2350 cm^?1 (CO₂) significantly decreased when the leaf was infected by powdery mildew. For the out layer the standard spectral variance between healthy leaf and infected leaf was 7.33 × 10², whereas it was 1.86 × 10⁴ for the deep layer; the standard spectral variance between out layer and deep layer for healthy leaf was 3.38 × 10³, whereas it was 1.84 × 10⁴ for infected leaf, which implied that both out layer and deep layer responded to powdery mildew infection. Combining spectral differences between healthy leaf and infected leaf and variances between out layer and deep layer, a presymptomatic detection of powdery mildew infection was successfully made, which provided an alternative option and noninvasive method for the fast diagnosis of powdery mildew infection on Rubus corchorifolius L.     

High-resolution coherent stokes Raman spectroscopy of theν 1 andν 3 bands of methane

Coherent Stokes Raman spectra of the ν₁ and ν₃ bands of CH₄ have been recorded in mixing two pulsed lasers (ruby and dye) of very good spectral and spatial quality. The results show a resolution of about 0.010 cm⁻¹ for a 10 Torr pressure, corresponding in great part to Doppler broadening.