T. Ippōshi

Hg content and thermal stability of the anodic sulfide films on Hg1−xCdxTe investigated by 30–40‐MeV O5+ ion backscattering

The Hg content of anodic sulfide films on Hg1−xCdxTe (MCT) were investigated for as‐grown and heat‐treated films by using 30–40‐MeV O5+ ion backscattering. Heat treatments were performed in a vacuum for 60 min at various temperatures up to 300 °C for the samples with x=0.20 and up to 350 °C for the samples with x=0.30 and 0.35. A significant Hg content of about 15 at. % of Cd was found in the as‐grown anodic sulfide film on MCT samples with x=0.20, 0.30, and 0.35. After heat treatment above 260 °C for x=0.30 and 0.35 and above 210–240 °C for x=0.20, the Hg atoms were removed from the films, and Hg deficient layers were formed near the interface region of the MCT crystal. This suggests that the residual Hg in the anodic sulfide films introduced during the sulfidization process plays an important role toward the degradation of the passivation properties of the sulfide film on MCT.

Atomic migration and surface evaporation of Hg in Hg1−x CdxTe crystals observed by 40‐MeV O5+ ion backscattering method

Dissociation and evaporation of Hg from the near‐surface region of Hg1−xCdxTe crystals was investigated, up to several microns, by means of 40‐MeV O5+ backscattering. Samples with x=0.18 and 0.32 were heat treated in a vacuum for 60 min at various temperatures up to 320 and 340 °C, respectively. The change of the backscattering spectra with the temperature of heat treatment indicated that the Hg atoms outdiffused partly from the near‐surface region of the crystals at higher temperatures than 280 and 320 °C for x=0.18 and 0.32, respectively. This behavior of outdiffusion is in contrast to the case of HgTe crystal.

Magnetophonon resonance recombination of hot carriers with emission of two TA-phonons in LPE-HgTe

Magnetophonon oscillations of longitudinal magnetoresistance of LPE-HgTe were investigated at 4.2 K under hot electron condition by using a second derivative method. Oscillations with 3–5 peaks were observed in 2–9T under electric field of about 1–4V cm-1. These peaks are interpreted as the first observation of magnetophonon resonance recombination of hot carriers accompanied by two TA-phonon emission. It is deduced for the first time that at low temperatures TA-phonon density of states has two peaks at 2.6 and 3.1 meV respectively.

Nonradiative carrier recombination processes of n‐Hg1−xCdxTe as determined by magnetic quantum oscillations

A mew method to determine the dominant process of nonradiative carrier recombination is proposed and demonstrated for n‐Hg1−xCdxTe (x≂0.2). This method is an application of the magnetic quantum oscillations of high electric field magnetoresistance which were observed successfully in a wide temperature range from 4.2 to 100 K by using a pulse technique and a second derivatives method, where Shockley–Read recombination as well as Auger recombination could be observed as an oscillatory behavior. The dominant origins of the oscillations could be clearly determined from the temperature dependence of the peak positions. Measurement and analysis were performed for a variety of samples with various carrier concentrations n and various electron mobilities μH (n=3×1014–2×1015 cm−3, μH=8×103–3×105 cm2/V s at 4.2 K). A competitive behavior of Shockley–Read and Auger processes and its sample dependence were clearly demonstrated.

Superconductivity Transition of High-Tc Y–Ba–Cu–O Systems with Multi- and Single-Phase; Tc and Hc2

Superconducting transition in the magnetic field up to 9T and the upper critical field Hc2 near Tc were investigated for Y1Ba2Cu3O7-δ with orthorhombic single phase, comparing with the Y–Ba–Cu–O samples with multi-phase. The upper critical field Hc2 is very large for single phase sample; the offset field Hc2off defined at 1% point is about 10T even at 76K and the slope (-dHc2/dT) for mid-point is 3.8T/K.

Hg content of anodic oxide films on Hg1−xCdxTe after heat treatment as measured by 40 MeV‐O5+ ion backscattering

The Hg concentration of anodic oxide films on Hg1−xCdxTe and its change after heat treatment were investigated by using 40 MeV‐O5+ backscattering. Heat treatment in a vacuum for 60 min was performed at various temperatures up to 350 and 400 °C, respectively, for the samples with x=0.19 and x=0.32. A significant Hg content in the as‐grown anodic oxide was found in accordance with the recent result of C. M. Stahle, D. J. Thomson, C. R. Helms, C. H. Becker, and A. Simmons [Appl. Phys. Lett. 47, 521 (1985)]. The Hg in the film gradually decreased with increasing heat treatment temperature up to about 290 °C and rapidly disappeared above 290 °C for both x=0.19 and x=0.32.

Magnetophonon resonance trapping of electron with emission of multi-phonon and magneto-Auger-recombination oscillation in n−Hg1-xCdxTe

Abstract A new effect of magnetic quantum oscillation of high electric field magnetoresistance due to the electron trapping with emission of multiple LO-phonons is reported together with the oscillation due to the Auger recombination. Oscillations were observed successfully in n−Hg1-xCdxTe (x ≅ 0.2) in a wide temperature range 4.2–100 K, by the combination of a pulse technique and a second derivative method. Analysis shows that, in the moderate quality samples, recombination through deep trap center is dominant at low temperatures while Auger recombination is dominant at the higher temperatures.

Superconducting Upper Critical Field Hc2 of High-Tc Y-Ba-Cu-O Compound System

Superconducting transition in the magnetic field up to 9 T and upper critical field Hc2 near Tc were investigated for several samples which have the nominal composition Y1-yBayCuOx with (a) y=0.60 or (b) y=0.65 and x undetermined. (a)- and (b)-samples show zero-resistance around 88 K and multi-phase and almost-single-phase behaviors, respectively, in the magnetic field, being consistent with a recently proposed model of YBa2Cu3Ox for a 90 K-range phase. In a (b)-sample, a very large value of (-dHc2/dT) of 3.0~3.5 T/K or 4.0~4.5 T/K was observed, depending on if Hc2 was taken at the 50% of the normal state resistance Rn or the 90%. Based on a theory assuming no paramagnetic limiting, this means Hc2(0) of 200 or 250 T, the highest one among the reported values.

LPE Crystal growth and magnetophonon resonance recombination of Hg1−xMnxTe

Abstract Single crystals of HgTe and Hg 1− x Mn x Te were grown on CdTe-substrates from the Hg-solution by lowering the temperature from 350 to 320°C in the sealed ampules. High quality LPE crystals were obtained by this method. In the semimagnetic semiconductor, Hg 1− x Mn x Te, magnetophonon oscillations of longitudinal magnetoresistance were investigated at 4.2 K under heated electron condition by using a second derivative method. Four distinct peaks were observed for the samples whose x -value is about 1%. These peaks are interpreted as due to the magnetophonon resonance recombination of heated electron and hole accompanied by two TA-phonon emission. The peaks of the same origin have been observed recently in HgTe. Peaks of spin-flip transition are well resolved in Hg 1− x Mn x Te, and the exchange integral between the conduction electron and the localized moment of Mn is deduced; β = 0.62 eV .

Auger recombination oscillation of magnetoresistance in Hg1−xCdxTe under heated electron and hole condition

Abstract A new effect of magnetic quantum oscillation of magnetoresistance due to Auger recombination is reported. Small oscillation of the longitudinal magnetoresistance of n Hg 1− x Cd x Te ( x = 0.195 ∼ 0.210) was investigated under heated electron and hole condition by d.c. method (up to about 10 V cm −1 ) using a second derivative method. 4 peaks were observed at 4.2 K under the electric field above 1 V cm −1 , while no peaks appeared in the ohmic magnetoresistance. Peak height increases with applied electric field. All peak positions coincide with a calculation based on an interpretation that the magnetoresistance peaks are due to the decrease of excess carrier through the onset of Auger recombination at the resonance magnetic field. Results of the similar measurement at higher temperatures up to 60 K can be also interpreted based on the same model.