Yang Pingxiong

Influence of annealing conditions on impurity species in arsenic-doped HgCdTe grown by molecular beam epitaxy

Based on our previous work, the influence of annealing conditions on impurity species in in-situ arsenic (As)-doped Hg1−xCdxTe (x ≈ 0.3) grown by molecular beam epitaxy has been systematically investigated by modulated photoluminescence spectra. The results show that (i) the doped-As acting as undesirable shallow/deep levels in as-grown can be optimized under proper annealing conditions and the physical mechanism of the disadvantage of high activation temperature, commonly assumed to be more favourable for As activation, has been discussed as compared with the reports in the As-implanted HgCdTe epilayers (x ≈ 0.39), (ii) the density of VHg has an evident effect on the determination of bandgap (or composition) of epilayers and the excessive introduction of VHg will lead to a short-wavelength shift of epilayers, and (iii) the VHg prefers forming the VHg-AsHg complex when the inactivated-As (AsHg or related) coexists in a certain density, which makes it difficult to annihilate VHg in As-doped epilayers. As a result, the bandedge electronic structures of epilayers under different conditions have been drawn as a brief guideline for preparing extrinsic p-type epilayers or related devices.

Impurity Activation in MBE-Grown As-Doped HgCdTe by Modulated Photoluminescence Spectra

Modulated photoluminescence spectra have been performed to investigate the impurity activation in MBE-grown As-doped Hg1−xCdxTe (x ≈ 0.3). The results show that the doped As mainly acting as donors in the as-grown samples can be fully activated as AsTe by two-stage anneals of 285°C/16 h + 240°C/48 h, of which the ionization energy has been determined to be about 10.5 meV, slightly smaller than that of intrinsic VHg (about 14.5 meV). However, the higher activation temperature (e.g. 400°C) at the first-stage can produce large numbers of excessive VHg and seriously deteriorate the quality of epilayers. This could give a brief guideline for preparing extrinsic p-type HgCdTe materials or devices.

Effects of substitutions of Nd 3+ for Sr 2+ on the properties of SrBi 2 Nb 2 O 9 ceramics and their mechanism

（Sr1-3x/2Ax/2Ndx）Bi2Nb2O9 （x=0，0.05，0.1 and 0.2） ceramics are prepared by traditional solid-reaction method， and effects of substitutions of Nd3+ for Sr2+ on the properties of SrBi2Nb2O9 ceramics and their mechanism are investigated. The results show that the temperature spectra of dielectric constant and loss for these Nd-doped samples are obviously characteristic of ion relaxor polarization. The partial substitution of Nd3+ for Sr2+ leads to the slight reduction in remanent polarization （Pr） and the increase in piezoelectric coefficient d33， which can be attributed to the increase in dielectric constant of samples according to ferroelectric thermodynamics theory. Raman spectrum shows that no change in the Curie temperature （TC） of （Sr1-3x/2Ax/2Ndx） Bi2Nb2O9 samples is observed， which might result from no appreciable variation in NbO6 octahedron distortion. For （Sr1-3x/2Ax/2Ndx） Bi2Nb2O9 ceramics， the substitution of Nd3+ for Sr2+ increases permittivity er， piezoelectric coefficient d33，and electromechanical coupling coefficient Kp and reduces mechanical quality factor Qm, but it does not change temperature coefficient of harmonic frequency value.