Yosio Nisida

Far-Infrared Absorption Spectra of Sb-Doped Ge at Low Temperature

The concentration dependence of far-infrared absorption spectra of antimony-doped germanium with 6×10 14 to 7×10 16 cm -3 , has been investigated in the wavelength range of 100 µm to 1 mm. In the excitation spectra, a higher energy line broadens faster with impurity concentration that a lower one, and disappears. In addition, the excitation lines shift slightly their position to lower energies and broaden in the low energy side with increasing concentration. Above 5×10 15 cm -3 , background absorption appears newly as a curve of gradual descent from the ionization limit toward low energies, and increases rapidly with concentration. This absorption spreads over the whole spectral range at 7×10 16 cm -3 , which would be responsible to the bolometric action. A qualitative discussion of the concentration effects is given. For sample having a small thickness (≈100 µm), the doublet structure of the excitation spectra was observed to change by surface treatment.

Shallow Donor Levels of Germanium in an Intermediate Magnetic Field

The magnetic field dependence of the shallow donor levels 1 s , 2 p 0 , 2 p -1 and 3 p -1 in germanium was calculated by using two types of variational wave functions each of which is appropriate either for weak magnetic fields or strong magnetic fields. In the range up to γ=0.7 ( H =43 kOe), it became evident that for the 1 s and 2 p 0 states the hydrogen-like wave functions give lower eigenvalues, whereas for the 2 p -1 and 3 p -1 states the harmonic oscillator-type wave functions become more appropriate above about 10 kOe. The effect of the magnetic field on the triplet and singlet ground states was evaluated with inclusion of the central-cell correction for both arsenic and antimony impurities. The optical transitions in the case of H //[111] and E ⊥[111] were considered.

Zeeman Spectra of Arsenic and Antimony in Germanium in an Intermediate Magnetic Field

The Zeeman spectra of arsenic and antimony donors in germanium were measured at liquid helium temperature with a static magnetic field along a [111] direction and up to 46 kOe. The Zeeman spectral lines of 2 p 0 , 2 p ±1 and 3 p ±1 were compared with the theory presented in a preceding paper. As a result, it was substantiated that the description of these donor levels can be well approximated by accounting only the longitudinal-axis component of the magnetic field for each velley, and also that the higher the levels the transformation from the weak approximation to the strong field approximation occurs at lower fields, The splitting of the ground states in the presence of a magnetic field was found to coincide with the theoretical prediction including the central-cell correction treated phenomenologically besides the magnetic field effect. On the basis of these comparison all the remaining absorption peaks were assigned to the hydrogen-like levels or the bound Landau levels.

Saturation of Impurity Cyclotron Resonance and Effect of 337 µm Radiation on Carrier Numbers and Mobilities in n-InSb

Effect of intense far-infrared radiation on magneto-absorption, photoconduction and photo-Hall effect on n -InSb containing 2.5×10 13 cm -3 electrons were investigated at liquid helium temperatures by using an HCN laser. Saturation of impurity cyclotron resonance (ICR) and enhancement of conduction-electron cyclotron resonance (CCR) with the radiation intensity were found. This can be explained by the effect of relaxation processes where the electrons excited to impurity state (010) drop to Landau state N =0 and accumulate there. The relaxation time for the ICR saturation was obtained as 7×10 -9 sec at 1.7 K. The photoconductivity and the photo-Hall effect were analysed on the basis of the two-band conduction model. The result demonstrates that with an increase of the radiation intensity the number of conduction electrons increases consistently with the proposed relaxation processes, and in addition the impurity-band mobility also increases.

Paramagnetic Relaxation of Chromium Ion in Ruby and Potassium Alum

Measurements have been made of spin-lattice relaxation times T 1 of single Cr ion impurities in ruby and alum, using the decay method at liquid helium temperature. In ruby, T 1 is dependent on the Cr ion concentration C , for specimens having more than 0.01% Cr, whereas in alum T 1 is nearly independent of C . The difference between them is explained in terms of spin-lattice relaxation via exchange pairs. The relaxation time T 1 in ruby varies as C -1 between 0.044% and 0.28%, which agrees with the theoretical prediction. At higher concentrations, T 1 decreases more rapidly with C and its temperature dependence becomes faster than T -1 . In very dilute crystals, T 1 at 4.2°K is 200 msec and 3 msec in ruby and alum respectively. The comparison of the values of T 1 for both crystals is given on the basis of the Van Vleck mechanism, and it is shown that the orbit-lattice interaction between Cr and ligand ions is larger in ruby than in alum.

Lattice Dielectric Constant of p-PbTe in the Far-Infrared Region

Magneto-transmission measurements by a strip-line method have been carried out on p-type PbTe whose hole concentration is 3×10 18 cm -3 at 4.2 K, in the wavelength range of 96.5 to 513.2 µm using an optically pumped far-infrared laser. It is shown that the observed transmission minima correspond to the dielectric anomaly of the ordinary ray. The frequency dependence of the lattice dielectric constant has been obtained using the reported values of the effective mass parameters. The result leads to the best fit values of the parameters: e 0 =1300, e ∞ =33 and ω TO =18 cm -1 .

Study of photo-magnetic effects and ESR in silicon doped with shallow centers using a SQUID magnetometer

Photo-magnetic (PM) effect is a change in magnetization which arises from spin reversal or orbital diamagnetism associated with optical excitation and subsequent relaxation processes. The PM effect on shallow impurities in silicon has been studied using a SQUID magnetometer. The SQUID-ESR has been also carried out to elucidate the origin of the PM effects. We have attempted to interpret the experimental results in terms of either the orbital diamagnetism of D - states or the unthermalized donor spins. Consequently we conclude that the PM effect arises from the unthermalization of donor spins which is induced by the spin-exchange scattering between donors and photoexcited hot carriers. Based on this model, rate equation approximation is discussed.