Sb mid-IR laser can be used in external configuration to achieve wide wavelength tuning range. At low temperature, gain media with band-edge wavelengths between 3.3 to 4 pm have been demonstrated with wavelength tuning up to ∼9% of the center wavelength. Power output from few tens of mW to 0.2-W peak, 20-mW average was achieved. Type-II Sb laser promises the possibility of such performance at higher temperature, e. g. 200 K. However, significant trade-off must be considered between tuning range and power and efficiency. Optimization requires consideration of both basic wafer design and cavity geometry.

Singly resonant type-il AgGaS2OPO yielded continuously tunable 3.9–11.3 µm idler output with slope quantum efficiency up to 41 % (absolute photon efficiency 22%). The OPO has sub-100 µJ threshold pump energies for nanosecond 1.06µm Nd:YAG laser pulses.

Direct comparison of performance has been done for a Pb1−xSnxTe(In) photodetector, a Si(Sb) BIB structure and a state of the art Ge(Ga) photoconductor in the integration cavity. The PblSnTe(In) photodetector shows several orders of magnitude higher responsivity S, then the Si(Sb) BIB at the wavelength λ ∼ 14 µm. Persistent photoresponse with SI ∼ 103 A/W at 40 mV bias and 1 s integration time at the wavelengths of, λ = 90 and 116 µm has been observed for the first time for the Pb1−xSnxTe(In) photodetector. This value is by a factor of ∼ 100 higher than the respective parameters of the Ge(Ga) photoconductor in the same conditions.

Photonic bandgap structures have received much attention as optical and infrared filters with controllable narrow-band absorbance. There is a need, however, for the same kind of control of the thermal emittance of surfaces for applications ranging from control of radiative heat transfer to gas absorption spectroscopy. We report on the fabrication of photonic bandgap structures on silicon surfaces using standard lithographic techniques. Substrate resistivity varied from n− to n+ and in some cases background surface emissivity was suppressed with a high reflectivity coating such as aluminum. We have measured the infrared reflectance and emittance of these patterned surfaces. Peak absorption wavelength and spectral purity (linewidth) correlate with photonic bandgap feature size and spacing as well as surface conductivity. We demonstrate band emission with a sharp short wavelength cut-off from these structures when heated.

Mid-infrared vertical cavity surface emitting lasers (VCSELs) using PbSe as the active material and broadband high reflectivity Pb1−xSrxSe/BaF 2 distributed Bragg reflectors (DBR) as bottom and top mirrors were grown by molecular beam epitaxy. By pulsed optical pumping, this first IV-VI semiconductor VCSEL operated up to 290K at a wavelength of 4.5 µm. Further optimization of such VCSELs could lead to room temperature continuos wave operation.

This paper describes a study of the photoresponse of long-wavelength (LWIR) and mid-infrared (MWIR) p-type GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) as a function of temperature and QWIP parameters. Using an 8x8 envelope-function model (EFA), we designed and calculated the optical absorption of several bound-to-continuum (BC) structures, with the optimum designs corresponding to the second light hole level (LH2) coincident with the top of the well. For the temperature-dependent study, one non-optimized LWIR and one optimized MWIR samples were grown by MBE and their photoresponse and absorption characteristics measured to test the theory. The theory shows that the placement of the LH2 resonance at the top of the well for the optimized sample and the presence of light-hole-like quasi-bound states within the heavy-hole continuum for the nonoptimized sample account for their markedly different thermal and polarization characteristics. In particular, the theory predicts that, for the LWIR sample, the LH-like quasi-bound states should lead to an increased Ppolarized photoresponse as a function of temperature. Our temperature dependent photoresponse measurements corroborate most of the theoretical findings with respect to the long-wavelength threshold, shape, and polarization and temperature dependence of the spectra.

Current-voltage, voltage-time, and noise measurements were taken on a three well, twenty period, InGaAs/A1GaAs quantum well infrared photodetector at low temperature and low constant current bias. Data from the voltage-time measurements exhibited random telegraph signal (RTS) which is a manifestation of a single electron capture/emission event. It thus contributes to generation-recombination noise of the device. A model is proposed that allows extraction of number of mobile carriers, continuum state electron mobility, electron emission times and trap activation energy from the RTS data. These parameters may then be utilized to predict the excess noise spectrum. Data from the noise spectral density measurements show 1/f like noise at frequencies below I kHz. It can be shown to be a sum of Lorenztian curves with various electron emission times.

The model proposed predicts that the local number of mobile charge carriers in any barrier section is less than 5 (total in the device around 300), there is nearly ballistic electron transport (mobility values around 3×105cm2/Vs), and the traps causing the RTS are in the barriers of the device and there are two of them in the device tested. The model applies to the linear mode of operation and assumes that the well regions are electron reservoirs, i.e. contacts, for the resistive barrier regions. The device is thus divided into a number of resistive portions in series. Each resistive portion is statistically independent from the others at low temperatures since the time the electrons spend in the wells is long compared to intra-well scattering times. This allows the electrons to fully thermalize and lose any statistical information from their previous continuum state trajectory.

The carrier concentration in narrow-gap semiconductors operating at room temperature is usually determined by thermal generation, not by doping. By reverse biasing a specially designed HgCdTe P+ - π - N+ heterostructure, the carrier concentrations in the narrow-gap π layer are held below the intrinsic concentration. Temperature dependent measurements of the reverse-bias current-voltage characteristics reveal that the devices operate as "usual" diodes below approximately 225 K. Above this temperature, the intrinsic carrier concentration increases, and the suppression mechanism appears in the I-V curves as negative differential resistance regions. The low-frequency noise performance of these devices, both in the forward bias and the reverse bias regime, as a function of temperature will be presented.

An optical coupling diffraction pattern for quantum well infrared photodetectors is developed using simulation. It provides high coupling efficiency and fabrication ease. Improved performance has been experimentally verified.

Optical absorption spectra of intersubband transitions in heavily proton irradiated n-type GaAs/AlGaAs multiple quantum wells were studied as a function of isochronal and isothermal annealing. The absorption spectra of intersubband transitions were depleted in samples irradiated with 1MeV proton doses higher than 1.0 × 1014 cm−2. Thermal annealing of the irradiated samples show that the intersubband transitions are recovered. The relatively lower annealing temperatures at which the recovery is observed indicate that the irradiation-induced defects that trapped the two-dimensional electron gas in the quantum wells are vacancy and interstitial related defects. Once these traps are thermally annealed the electrons are released back to the quantum wells, resulting in the recovery of the intersubband transitions.

In this paper, the theoretical study of intersubband transitions in quantum well infrared photodetectors (QWIPs) applying the eight bands k.p model incorporated with envelope function approximation is described. The focus of the work is on the intersubband transition in n-type IIIV QWIP based on AIGaAs/GaAs and AlGaAs/InGaAs material system, with particular emphasis placed on the physics of TE excited transition and the improvement of resulted absorption. Various theoretical absorption spectra of the two material systems are compared, the distinct mechanisms of the intersubband transition for the two material systems are proposed. Possible ways of improving on the absorption for such excitation are also investigated and discussed.

Be-doped InGaAs/AIGaAs multiple quantum well (MQW) structures, grown by solid-source molecular beam epitaxy with different doping concentration in the wells, were investigated by xray diffraction and transmission electron microscopy (TEM). Some features have been observed. (1) The MQW mean mismatch increases from 1.176 × 10−3 to 1.195 × 10−3 and 1.29 × 10−3 for the structures with doping concentration of 1 × 1017 cm−3, 1 × 1018cm−3and 2 × 1019 cm−3 in the wells, respectively. (2) The period of the MQW also increases with doping density. (3) The intensity of the first order satellite in the rocking curves decreases as the Be concentration is increased, indicating that indium diffusion in the heavily doped wells is likely more significant than that in the lightly doped ones. (4) The full width at half maximum of the zero-order satellite peak becomes widened as doping concentration increases, indicating that high Be-doping in the well likely deteriorates the interfaces of the multiple quantum well stacks. In addition, TEM measurement is conducted and clear pictures on well and barrier layers of the structures are observed. The information obtained is of great value for the design of p-doped quantum well infrared photodetectors.

A Schottky type infrared detector fabricated on a p-type Si1−xGex substrate has a higher cut-off wavelength than one on a pure Si substrate because the barrier height of the Schottky junction on p-type Si1−xGex decreases with the Ge content and the induced strain in the Si1−xGex layer. We have studied the effect of the strain relaxation on the internal photoemission and I-V characteristics of a Pt/Si1−xGex Schottky junction with x=0.14. It is shown that the cut-off wavelength of the diode made on a strained Si0.86Ge0.14 layer is higher than that on a Si substrate as expected. This shows the possibility of tuning the range of these detectors in the mid-infrared region. However, the thermal relaxation in the Si0.86Ge0.14 layer is found to reduce the cut-off wavelength to lower values, showing that the difference between the Fermi level of the metal and the valence band edge increases with the layer relaxation. This effect should be taken into account when a Schottky type infrared detector is manufactured on a strained Si1−xGex film. I-V characteristics of the junctions also indicate an increase of the barrier height with the relaxation of Si1−xGex. These results demonstrate the band edge movements in a Si ixGex layer experimentally agree with the expected changes in the band structure of the Si1−xGex layer with strain relaxation.

The photoluminescence spectra, defect composition and optoelectronic properties of chlorine doped CdTe monocrystals, thick layers and thin films are investigated. It is supposed that the complex defect (VCd-2ClTe) is a neutral defect that causes high resistivity of Cl doped CdTe. This complex can dissociate into two charged defects (VCd-ClTe) and ClTe at 300 K. Acentre (VCd-ClTe) is a stable defect that is responsible for p-type conductivity of Cl doped CdTe. Depending on the C1 concentration high resistivity, high photoconductivity or high p-type conductivity can be formed in CdTe that is only chlorine doped.

Galvanomagnetic properties and photoconductivity kinetics of Pb1−xGexTe(x≤0.04) alloys doped with Yb have been investigated. The alloys exhibit high infrared photosensitivity at temperature under 40 K; at helium temperature, the effect of persistent photoconductivity has been observed. The photoconductivity kinetics after terminating of infrared illumination consists of a fast and a long-term relaxation regions. We explain the observed effects by a capture of electrons into the Yb-induced states, that are subjected to the Jahn-Teller instability. The parameters of the Jahn-Teller states are estimated.

Silicon-gemanium is a promising materials system for delivering near-IR photodetection on the ubiquitous silicon substrate. The 4% lattice mismatch leads to biaxial strain for SiGe films grown coherently on (100) Si substrates, which both extends the long wavelength detection limit by reducing the band gap and defines the critical thickness for the SiGe film. We have studied the use of strained-layer superlattices grown on high quality relaxed SiGe buffers. Graded buffers are ideal virtual substrates for achieving a complete range of compositions and strains for GeSi alloys. A physical model has been created to map out the absorption coefficient as a function of Ge fraction and (100) biaxial strain. Based on calculated absorption spectra as a function of composition and strain, we have designed and grown a Ge/Ge0.5Si0.5 strain-balanced superlattice on a high quality Ge0.75Si0.25 relaxed buffer using UHV-CVD. The strain-balanced superlattice has an effective absorption coefficient of 5000 cm−1. The relaxed buffer serves as a virtual substrate with relatively low threading dislocation density (106 cm-−2). The effect of the threading dislocations on the leakage current of P-I-N junctions is also investigated. Electron beam induced current (EBIC) is used to determine the dislocation density of SiGe relaxed buffer junctions grown with different grading rates. Mesa isolated devices are used to determine bulk leakage current densities for the SiGe junctions. The bulk leakage current density scales directly with the dislocation density. Bulk leakage currents density per dislocation length (2×10−5 A cml) agrees with deep level transient spectroscopy (DLTS) determined literature values for SiGe capture cross-section and defect density per dislocation in Si.

The ternary semiconductor GaAs1−xNx with 0 < x < 0.3 can be grown epitaxially on GaAs and has a very large bowing coefficient. The alloy bandgap can be reduced to about 1.0 eV with about a 3% nitrogen addition. In this work, we measlired the internal spectral response and recombination lifetime of a number of alloys using the ultra-high frequency photoconductive decay (UHFPCD) method. The data shows that the photoconductive excitation spectra of the GaAs0.97N0.03 alloy shows a gradual increase in response through the absorption edge near Eg. This contrasts with most direct bandgap semiconductors that show a steep onset of photoresponse at Eg. The recombination lifetimes frequently are much longer than expected from radiative recombination and often exceeded 1.0 µs. The data was analyzed in terms of a band model that includes large potential fluctuations in the conduction band due to the random distribution of nitrogen atoms in the alloy.

Energy levels of the shallow acceptor states have been calculated for center-doped Si/Si1−xGex/Si quantum wells (QWs). The impurity states were calculated using an effective-mass theory that accounts for valence-band mixing as well as the mismatch of band parameters and dielectric constants between well and barrier materials. Acceptor binding energies and splitting between the acceptor 1S3/2(Γ7) and 1S3/2(Γ6) ground states were studied at various Ge concentrations and well widths. The results are discussed in comparison with the recent experimental data from the lateral transport measurements in boron-doped Si/SiGe quantum wells.

We have grown high-quality Ge epilayers on Si using two-step ultrahigh vacuum/chemical-vapor-deposition followed by post-growth cyclic thermal annealing. Cyclic annealing was effective in reducing threading dislocation densities. The annealing process was improved by optimizing the dislocation velocity. We fabricated and tested metal-semiconductor-metal planar photodetectors using Ge epilayers grown on Si. Our measurement showed an improvement in the photodetector performance as a result of the improved materials quality. The process described in this paper for making high-quality Ge on Si is uncomplicated and can be easily integrated with Si CMOS processes.

We report on increasing the pulse length and repetition rate of p-type germanium lasers through miniaturization, increased electric field uniformity, and improved cooling. We have recently demonstrated that it is possible to improve the electric field uniformity necessary for an efficient laser and at the same time decrease the electrical input power by using a geometry with d/L>>1, where d is the distance between electrical contacts and L is the length in the direction of the Hall field. In order to achieve good heat sinking along with a large d/L ratio, we have developed a new, planar contact geometry. Attaching an undoped, high-resistivity, single-crystal Si heat sink to the base of the Ge planar contact laser increases the duty cycle by a factor of 5.5. In order to further decrease the input power by decreasing the volume of laser crystals in the planar contact geometry, we show as a proof-of-concept the use of polished strontium titanate single crystals as electrically insulating far-infrared mirrors based on restrahl band reflection. The physical phenomena underlying these improvements in this novel geometry will be discussed.