Search

Internal quantum efficiency (IQE) of InGaN/GaN UV LEDs with patterned sapphire substrates (PSS) was investigated using electroluminescence (EL) and photoluminescence (PL) methods. The physical mechanisms that affect temperature-dependent EL efficiency as a function of injected carrier density were deduced. In order to reduce the density of non-radiative recombination centers to improve quantum efficiency, improvement of crystal quality and reduction in the number of defects are necessary. PSS LEDs showed better EL characteristics than non-PSS LEDs because of the improved epitaxial quality. Contrary to PL IQE, EL IQE was significantly affected by carrier injection efficiency, especially at low temperature when high bias voltage was applied to the p–n junction.

We have investigated the influence of the TEGa flow on the optical and structural properties of InGaN/GaN multiple quantum wells (MQWs) with an indium composition around 20%. The samples with five-pairs InGaN/GaN MQWs were grown on sapphire substrates by metalorganic chemical vapor deposition. Photoluminescence spectra at 8 K showed that the MQWs grown with a low amount of TEGa flow gave a strong single peak and a higher emission energy. High-resolution X-ray diffraction measurements showed a deterioration of the InGaN/GaN interfaces in the sample grown with the large TEGa flow. The luminescence thermal quenching characteristics suggested that more structural defects acting as non-radiative recombination centers formed in the MQWs when the TEGa flow increased. The results indicate that decreasing the TEGa flow help to build up a new growth balance during the growth of InGaN wells, leading to less structural defects, more homogeneous indium distribution and the abrupt MQWs interfaces.

We have demonstrated that Mg is a controllable acceptor element for p-type GaAsN alloys grown by solid-source molecular-beam epitaxy (MBE), where a hole concentration has been realized up to 1.5×10 20 cm −3 and has been controlled along the vapor pressure curve of Mg using a standard effusion cell. In addition, electrical and luminescence characterizations have been investigated for GaAsN:Mg samples grown by solid-source MBE. The activation energy of Mg for the GaAsN:Mg samples is close to the impurity energy of Mg in GaAs (28 meV). Thus Mg is a very shallow acceptor element for GaAsN alloys. From photoluminescence (PL) measurements, the integrated PL intensity drastically increases with increasing a hole concentration up to 8.6×10 19 cm −3 at 300 K. This result suggests that the hole concentration can increase up to 8.6×10 19 cm −3 without significantly increasing the non-radiative recombination centers related to Mg doping when Mg is the acceptor element.

Epitaxial lateral overgrowth (ELOG) of a -plane GaN on r -plane sapphire with stripe orientations parallel to [0 0 0 1], [ 0 1 1 1 ], and [ 0 1 1 0 ] has been investigated. The emission from ELOG stripes with different orientations and from different growth facets has been compared by spectrally and spatially resolved cathodoluminescence and by temperature-dependent photoluminescence measurements. A reduction in the nonradiative recombination rate by the ELOG process is clearly observed. For all stripe orientations the ELOG wing regions exhibit increased radiative emission intensities compared to the window areas, indicating a reduced dislocation density in the overgrown areas. The highest increase of the near band edge (NBE) emission is observed in the wing regions for stripes parallel to [ 0 1 1 0 ]. In this region, the density of basal plane stacking faults (BSFs) is also reduced. NBE emission is detected up to temperatures of 250 K.

Photoluminescence (PL) of Si nanocrystals with annealing in CO2 was studied using the continuous and time-resolved PL measurements. The PL intensity enhances as annealing temperature increases, which is attributed to passivation of the nonradiative recombination centers. As the annealing temperature is 950 °C the PL intensity has a maximum value, which increases about a factor of 3 than that of the untreated sample. Based on the emission energy dependence of the PL decay time, the depth of carrier localization is found to increase after the annealing in CO2. We suggest that the oxygen atoms desorbed from CO2 diffuse to react with Si nanocrystals and introduce localized states at the Si/SiO2 interface.

Nitrogen flow rate dependence of InGaN growth mechanism on sapphire (0 0 0 1) was studied. The indium content of the InGaN layer can be controlled by changing the nitrogen supply rate by structural and optical investigations. In case of lower nitrogen flow rate, the formation of phase separation due to dissociation of InN and condensation of indium on the growing surface were observed. In case of higher nitrogen flow rate (under N-rich condition), on the other hand, the indium content became uniform and the photoluminescence (PL) emission showed single peak. It is considered that the causes of phase separation formation were suppressed and nonequilibrium condition was enhanced by the increase of the nitrogen supply rate and the growth rate. Judging from the estimated thermal activation energies and degree of fluctuation in the indium content by PL line-width, however, the non-radiative recombination centers within the spontaneously formed potential wells as well as in the extended states were formed in case of excess nitrogen supply rate. The structural defects that were caused by the suppression of the surface migration of group-III atoms with excessive activated nitrogen might have worked as non-radiative recombination centers. Thus, a slightly N-rich condition is desirable for the realization of the uniform InGaN alloy composition and the high optical quality, especially at relatively high growth temperature.

Self-assembled InAs bi-quantum-dot molecules (BQDMs) on GaAs (0 0 1) have been achieved using gas-source molecular beam epitaxy (GSMBE) and characterized by atomic force microscopy (AFM) and photoluminescence (PL) measurements. After the initial InAs quantum dots are partially capped with GaAs and followed by deposition of InAs, BQDMs are formed. Photoluminescence spectra of BQDMs can be described by two Gaussian-fitted curves at low temperature due to two different dot sizes. This is consistent with dot height histograms obtained from AFM images of BQDMs. For PL intensity, thermal quenching is observed at temperatures above 100 K. The activation energy of BQDM PL corresponds to nonradiative recombination due to defected-related states and potential fluctuation.

MgSe/BeZnSeTe II–VI compound superlattices (SLs) were grown on InP substrates by molecular beam epitaxy (MBE). In the growth, Zn molecular beam irradiation was performed at each hetero-interface between MgSe and BeZnSeTe layers to suppress in-plane compositional fluctuation of the BeZnSeTe layers and to enhance steepness of the interfaces. The Zn irradiation effect was systematically investigated changing the Zn irradiation time. As a result, it was found that structural and optical properties of the SLs strongly depended on the Zn irradiation time. Explicit high-order X-ray diffraction (XRD) satellite peaks appeared by introducing the Zn irradiation, which means the interface steepness was improved. In photoluminescence (PL) measurements at room temperature (RT), single peak emissions around 520 nm were observed. PL intensities at 15 K and RT strongly depended on the Zn irradiation time, and they were maximized when the Zn irradiation time was 4 s. The supply amount of the Zn irradiation for 4 s corresponds to about two-monolayer growth. From the dependencies of the PL intensity, it was shown that appropriate Zn irradiation was effective for both increase in the radiative recombination rate and decrease in the non-radiative recombination rate.

The metrological capability of the picosecond four-wave mixing (FWM) technique for evaluation of the photoelectrical properties of GaN heterostructures grown on sapphire, silicon carbide, and silicon substrates as well as of free-standing GaN films is demonstrated. Carrier recombination and transport features have been studied in a wide excitation, temperature, and dislocation density (from ∼10 10 to 10 6 cm -2 ) range, exploring non-resonant refractive index modulation by a free carrier plasma. The studies allowed to establish the correlations between the dislocation density and the carrier lifetime, diffusion length, and stimulated emission threshold, to reveal a competition between the bimolecular and nonradiative recombination, and to verify the temperature dependence of bimolecular recombination coefficient in the 10-300 K temperature range. It was shown that the FWM technique is more advantageous than the time-resolved photoluminescence technique for determination of carrier lifetimes in high quality thick III-nitride layers.

(GaIn)(NAs)/GaAs multi-quantum-well heterostructures are grown by metal organic vapor phase epitaxy at low temperatures and are subsequently annealed in the reactor to optimize optoelectronic properties. Detailed optical and structural studies of the properties of the material, which change upon annealing under different As-stabilization as well as at different temperatures, reveal that there are two major effects of the anneal. The first one is the blue-shift of the fundamental band gap of the material, which can be attributed to a local change in the group-III environment of the nitrogen atoms. The second observation is a strong increase in photoluminescence (PL) intensity and decrease in PL linewidth upon anneal in H2-ambient, which can be attributed to the removal of non-radiative defects in the material. Chain-like N-ordering in growth direction, which induces strong inhomogeneous strain fields in the material and which can be dissolved upon anneal in H2-ambient might also act as one of the main non-radiative recombination centers in the (GaIn)(NAs) material system.

Cathodoluminescence (CL) mapping and selective-etching techniques were used to characterize defects in free-standing bulk GaN substrates prepared by hydride vapor phase epitaxy. Melton KOH–NaOH (1:1) solution was found to be effective to produce etch pits on bulk GaN with density close to the anticipated dislocation density. Under preferred etching and measurement conditions, a strong correlation between CL mapping and selective-etching techniques for revealing defects in the bulk GaN was demonstrated. All structural defects causing etch pits are confirmed to be non-radiative recombination centers showing dark contrast in CL map, while CL mapping could give additional information about certain internal defects underneath the GaN top-surface. The clear correlation established in this comparative study provides strong support for the viability of using both techniques for evaluating bulk GaN.

Near-ultraviolet InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown homoepitaxially on a free standing GaN substrate exhibited improved microstructural, electrical and optical properties compared to similar devices grown on sapphire. In contrast to strong tunneling behaviors in the LEDs on sapphire, thermally activated currents were observed at both forward and reverse biases in the LEDs on GaN. At low injection currents, the quantum efficiency of the LEDs on GaN was much higher, suggesting reduced nonradative recombination centers. At high driving currents, the homoepitaxial LEDs greatly outperformed the devices on sapphire as a result of improved material quality, heat dissipation and current spreading. These results show the promise of homoepitaxially grown GaN-based LEDs for solid-state lighting applications.

Ultrafast differential transmission measurements on a series of InN epilayers, grown by molecular beam epitaxy, have been employed to determine the carrier lifetimes and to probe the carrier recombination dynamics at room temperature. Differential transmission spectra reveal a peak energy of ∼0.7 eV on these samples, supporting the existence of the narrow band gap of InN. In addition, we observed a fast initial hot carrier cooling followed by a slow recombination process after pulse excitation. Carrier lifetimes ranging from 48 ps to 1.3 ns have been measured in these samples. An inverse proportionality between the carrier lifetime and the free-electron concentration was observed, suggesting that the donor-like defects or impurities may stimulate a formation of non-radiative recombination centers, reducing the carrier lifetime.

AlGaInP/GaInP multiple quantum well laser structure was grown by low-pressure metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine. Photoluminescence (PL) measurements were performed from 10 to 230 K. The PL energy increased with temperature from 10 to 70 K and decreased above 70 K. The former was attributed to thermal activation of trapped carriers due to localization in the quantum wells, while the latter was attributed to temperature-induced band-gap shrinkage. The PL intensity as a function of temperature was fitted by employing two nonradiative recombination mechanisms with good agreement, resulting in two activation energies that correspond to losses of photogenerated carriers to nonradiative centers.

The relationship of the threading dislocations (TDs) and InGaN-based quantum well (QW) optical characteristics is studied by temperature-dependent photoluminescence, high-resolution X-ray diffraction and atomic force microscopic. It is found that TDs deteriorate the QW interfacial abruptness, and can enhance the localization effect. Temperature-dependent photoluminescence measurements give evidence that the TDs act as nonradiative recombination (NR) centers in InGaN active layer. According to these results, it is inferred that the influence of TD on the optical properties of InGaN-based QW depends on the competition of localization induced by TDs and the NR effect of TDs.

Optical and structural characterizations were conducted on an InGaAsN quantum well (QW) with large energy bandgap barrier material consisting of InGaAsP (Eg ¼ 1:62 eV) grown by metalorganic chemical vapor deposition. A growth pause annealing technique substantially improves both the structural and the optical quality of the QW. With an optimum growth pause of 14 s, surface roughness reduces by 50% and photoluminescence intensity increases 25 times compared with the sample undergoing a 3-s growth pause. No significant emission wavelength blue shift was observed, indicating this growth pause annealing process involves a mechanism different from that of the conventional post-growth thermal annealing of InGaAsN QW. Preliminary results on InGaAsN-active diode lasers employing InGaAsP barrier material indicate performance is limited by nonradiative recombination. r 2004 Elsevier B.V. All rights reserved.

High performance of multi-quantum well (MQW) solar cells depends not only on the material quality ensuring minimum non-radiative recombination losses expected at the heterointerfaces, but also on the escape rate of photogenerated carriers out of QWs with minimum radiative losses within QWs. We investigated potentially modulated MQW solar cell structures, for which the MQW structure is modified from a series of conventional square-shaped QWs to “step-like” potentially modulated QWs. We fabricated “two-step” and “three-step” MQWs introduced into the intrinsic region of GaAs p–i–n solar cells by atomic H-assisted molecular beam epitaxy (H-MBE). Compared with a square-shaped MQW cell, a three-step modulated MQW cell having the same average potential well depth showed photoluminescence characteristics with a smaller thermal activation energy and higher average carrier temperature and indicated that photogenerated carriers escape out of QWs more efficiently in this type of structure.

The growth of high nitrogen content InGaAsN/GaAs single quantum well (SQW) for 1.55 μm applications on GaAs substrates using solid source molecular beam epitaxy and radio frequency plasma nitrogen source is reported. The nitrogen composition was determined using an X-ray diffractometer combined with dynamic simulation. The crystal and optical qualities of highly strained InGaAs/GaAs SQW grown at low temperature can be significantly improved by nitrogen incorporation due to reducing the lattice mismatch. Without the formation of additional nonradiative recombination in InGaAsN SQW with nitrogen composition up to 4.1% which corresponds to wavelength of 1.46 μm was achieved. The longest room-temperature PL peak wavelength obtained in this study is 1.59 μm by increasing the nitrogen composition up to 5.3%. And, the photoluminescence intensity of high nitrogen content InGaAsN SQW can be improved significantly by decreasing the growth temperature due to suppression of the phase separation of InGaAsN alloy. Our results show the potential for the fabrication of 1.55 μm InGaAsN QW lasers on GaAs substrates.

We investigated the optical and electrical quality of Mg-doped In x Ga 1− x N (0⩽ x ⩽0.045) grown by metalorganic chemical vapor deposition with different In and Mg contents. The band edge emission of p- In x Ga 1− x N layer depended on the Mg incorporation. The emission intensity of InGaN band edge peak was drastically reduced with increasing Mg incorporation, indicating that the concentration of nonradiative recombination centers increased with Mg doping concentration in InGaN layer. Mg-related emission of p-In x Ga 1− x N was changed from the shallow acceptor level to deep acceptor level as Mg concentration increased. Additionally, photoluminescence spectra showed that the band to acceptor emission energy E (e − , A 0 ) decreased with increasing In composition under the same Mg concentration of 2×10 19 /cm 3 . The activation energy of Mg obtained from PL spectra is reduced from 170 to 123 meV with increasing In content. Although the intensity of InGaN band edge emission and the donor–acceptor pair emission drastically decreased with increasing Mg concentration, the hole concentration increased up to 2.5×10 18 /cm 3 with Mg concentration for p-In 0.045 Ga 0.955 N.

We reported the effect of trimethylindium (TMIn) flow rate in the barrier layer on the structural and optical properties of InxGa1-xN/InyGa1-yN multiple quantum wells (MQWs) grown on (0001)-oriented sapphire substrates by low-pressure metalorganic chemical deposition (LP-MOCVD). It was found that the change of TMIn flow rate dramatically influences the interface quality and optical properties. Temperature-dependent photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD) measurements provide proof evidence that the increment of TMIn flow rate deteriorates the interfacial abruptness, decreases the emission wavelength (blue shift) and the efficiency of nonradiative recombination process. (C) 2003 Elsevier B.V. All rights reserved.

Self-organized InAs quantum dots (QDs) have been fabricated by molecular beam epitaxy and characterized by photoluminescence (PL). For both single- and multi-layer QDs, PL intensity of the first excited state is larger than that of the ground state at 15 K. Conversely, at room temperature (RT), PL intensity of the first excited state is smaller than that of the ground state. This result is explained by the phonon bottleneck effect. To the ground state, the PL intensities of the multi-layer QDs are larger than that of the single-layer QDs at 15 K, while the intensities are smaller than that of the single-layer QDs at RT. This is due to the defects in the multi-layer QD samples acting as the nonradiative recombination centers. The inter-diffusion of Ga and In atoms in the growth process of multi-layer QDs results in the PL blueshift of the ground state and broadening of the full-width at half-maximum (FWHM), which can be avoided by decreasing the spacers' growth temperature. At the spacers' growth temperature of 520degreesC, we have prepared the 5-layer QDs which emit near 1.3 mum with a FWHM of 31.7 meV at RT, and 27.9 meV at 77 K. (C) 2002 Published by Elsevier Science B.V.

The effects of hydrogen treatment for polycrystalline nitrogen-doped cuprous oxide (Cu 2 O) thin films on their electrical and optical properties were studied. Although the emission was not observed before the treatment by hydrogen plasma, near band edge emission of Cu 2 O at around 680 nm was observed after the treatment. This result indicates that the non-radiative recombination centers possibly existing on and in polycrystalline grains are passivated by hydrogen. The hole density was controlled from the order of 10 16 –10 18 cm −3 by hydrogen treatment. The control of the hole density in such a range was achieved for the first time. From these results, hydrogen treatment was found to be very effective to passivate defects and improve electrical and optical properties of polycrystalline Cu 2 O.

We report a comparison of the plasma-assisted MBE growth of polar (0 0 0 1) and semipolar (1 1 −2 2)-oriented InGaN/GaN quantum dots (QDs) grown simultaneously on GaN templates. The photoluminescence (PL) from semipolar QDs shows a systematical blueshift in comparison to the respective polar samples. Notwithstanding the variation in the internal electric field between the two samples, the observed shift in the PL spectrum can be attributed to the different In incorporation in the two crystallographic orientations. The evolution of PL intensity with temperature confirms the three-dimensional carrier confinement, which results in an attenuation of nonradiative recombination effects in comparison with quantum well structures.

The origin of a deep emission band (2.25 eV) with a quite strong electron phonon interaction in MBE grown ZnSe 1-x Te x alloys has been investigated and discussed. The emission band can be observed at the Te content x of about 0.03. The zero phonon energy of the emission hand coincides with the ZnSe-like exciton (2.79 eV) at low temperature. The Huang-Rhys parameter S and the phonon energy at the excited state are estimated as 23 and 24 meV. respectively, indicating strong electron phonon coupling with the Frank Condon shift of 550 meV.

Photoluminescence (PL) and piezoelectric photoacoustic (PPA) spectra have been studied at low temperatures for nondoped and N-doped ZnSe epitaxial layers grown by molecular beam epitaxy. Deep emission bands observed in nondoped ZnSe are disappeared with nitrogen doping in the PL spectra. On the other hand, new nonradiative signals appear with nitrogen doping in the PPA spectra. This indicated that nonradiative carrier recombination centers are introduced by the nitrogen doping process in molecular beam epitaxy growth.

Ionisation (2+-to-3+ or 1+) and intra-shell transitions of iron in bulk crystals of ZnS, ZnSe, CdSe and in their alloys are studied. The results of these studies allow us to verify the recent theoretical predictions on universal reference levels due to transition metal ions and to explain the nature of Fe-related nonradiative transitions in ZnSe. We also demonstrate limitations of the Ludwig–Woodbury model for the description of intra-shell transitions of Fe 2+ .

It is known that InGaN LED can emit brilliant light though ∼10 8 cm −2 of threading dislocations exists in the active layer. Recently, the origin of defect-insensitive emission was studied [Chichibu et al., Nature Materials 5 (2006) 810] and elucidated that –In–N– zigzag atomic chains act as effective radiative recombination centers. Relationships between growth conditions and atomic arrangements in InGaN thin films were investigated by Monte Carlo simulation in the present study. Estimated density of –In–N– zigzag atomic chains in the grown films are more than 10 20 cm −3 which is large enough compared with the density of non-radiative recombination centers, i.e., 18 cm −3 , evaluated by Chichibu et al.

We have studied the effect of oxygen incorporation into AlGaInP on carrier recombination in GaInP/AlGaInP double heterostructures (DH) grown by MBE using a solid phosphorus valved cell. It was found that photoluminescence efficiency and interfacial recombination velocity of the DH were determined by residual oxygen concentration in the AlGaInP layers. The non-radiative recombination rate in AlGaInP was proportional to the oxygen concentration. We achieved AlGaInP with oxygen concentrations below 4 × 10 16 cm -3 (the detection limit of the SIMS measurement), nonetheless decay of the carriers in the DH was still governed by interfacial recombination. There was a discrepancy in interfacial recombination velocity as a function of oxygen concentration between samples previously grown by MOCVD and our samples currently grown by MBE.

Si-doped GaN layers were grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD) and characterized by using electron beam-induced current (EBIC) and molten KOH etching. Dark spot densities in EBIC image are be 1.0 and 1.2×10 8 cm −2 depending on the accelerating voltage. The dark spots in EBIC image correspond to recombination centers. When we compare dark spot density with etch pit density revealed molten KOH, this is the same order as the EPD revealed by molten KOH. We confirm there are many dislocations which influence recombination of minority carriers in the layers.

We have fabricated deep etched Cd 0.35 Zn 0.65 Se/ZnSe quantum wires with lateral extensions down to 14 nm. The wires were defined by electron beam lithography and a low damage wet chemical etch process. Time-integrated and time-resolved photoluminescence spectroscopy was used to study excitonic properties in ultranarrow wide bandgap quantum wires. Lateral quantization causes a blue shift of the photoluminescence emission of up to 17 meV with respect to the 2D reference. A low temperature (T= 2 K) lifetime of about 110 ps was found, almost independent of the wire width. At room temperature, non-radiative sidewall recombination reduces the exciton lifetime from 330 ps for the 2D reference to about 21 ps in the case of a 28 nm wide wire.

We present data in this paper which demonstrate that the luminescence efficiency of p-type ZnSe : N grown by molecular beam epitaxy using a remote RF plasma source is a strong function of doping concentration and that in moderately to heavily doped material (corresponding to N A - N D ⩾ 2 × 10 17 cm -3 ) significant concentrations of non-radiative recombination centers strongly limit the luminescence efficiency of the material. Such data were obtained by performing real-time, in situ cathodoluminescence intensity measurements during epilayer growth for variously doped epilayers.

Optical properties of the InGaAs/InP double-heterostructures (DHs) selectively grown in the striped channels by chemical beam epitaxy (CBE) were characterized by a photoluminescence (PL) method at room temperature and at 77 K. It was found that the alloy composition of InGaAs near the stripe edge was different from that at the stripe center. A broad PL brand at 0.72 eV was observed in the 77 K PL spectra from the selectively grown DH. This transition was unambiguously identified as defect related.

The discrepancy between the measured photoluminescence spectra of Si 1-x Ge x strained alloy layers originating from molecular beam epitaxy (MBE) and chemical vapor deposition (CVD) processes is investigated. Sharp excitonic band edge luminescences are observed for films by both growth techniques. For certain films grown by MBE, the photoluminescence spectra contain an additional broad alloy band luminescence at low energy. Deuterium passivation of the MBE layers is shown to annihilate the broad band luminescence and to increase the band edge luminescence intensity. These results are compared with the more intense band edge luminescence signals from CVD layers for which abundant hydrogen radicals are usually present during the deposition

The crystalline quality of ZnSe epitaxial layers (over-epilayers) on top of Li + -implanted ZnSe epilayers grown by atmospheric pressure MOVPE is governed by the radiation and annealing damage. The PL intensity of the band-edge emission (461 nm) at 300 K is affected by the damage remaining in the implanted epilayers. The damage affects the PL properties of the over-epilayers. This suggests that the non-radiative recombination centers produced probably propagate into the over-epilayers. The radiation damage cannot be removed completely by annealing under H 2 or N 2 atmospheres alone, and is made worse by annealing at high temperature. Since annealing in an atmosphere containing Zn or Se vapor restores the PL properties, at 300 K, of an over-epilayer substantially to that of an as-grown epilayer, it is suggested that the non-radiative recombination centers are related to native defects, particularly Zn vacancies.

Transport and photoconductive properties of p-Hg 0.8 Cd 0.2 Te and n-Hg 0.7 Cd 0.3 Te have been studied at temperatures between 16 and 250 K. The crystals showed different lifetimes than that observed in n-type Hg 0.8 Cd 0.2 Te, where Auger recombination was found as the dominating recombination mechanism. The minority carrier lifetime in p-Hg 0.8 Cd 0.2 Te could be explained by Shockley-Read recombination involving a deep donor-like centre located about 6 meV above the valence band edge. In n-type Hg 0.7 Cd 0.3 Te radiative recombination was found to dominate at temperatures above 40 K. Obviously the band gap of this composition is too wide for an effective Auger mechanism. Below 40 K trapping of minority carriers occurs and one observes two life time constants. Here the recombination mechanism was identified as recombination via defects in the band gap.

The properties of MZT are analyzed according to the concept of stability after specifying it through considerations related to the Zn-Te bond. in comparison with MCT, direct single crystal growth is shown possible by THM. The ingots are of better longitudinal homogeneity and the crystals of better crystalline quality. Lower interdiffusion coefficients are found from interdiffusion experiments the results of which are interpreted by introducing a large term of interaction between cations. The better stability of the surfaces is demonstrated from electrochemical experiments and the better bonding strength from hardness data. An intense absorption excitonic line, in the absorption spectra, accounts for less non radiative recombination. Excellent implanted IR photodiodes confirm the importance of this material.