Degradation in devices of III-V compound semiconductors, especially of GaAs, is reviewed to give a whole scope on this complicated phenomenon. Factors which affect the degradation are studied at the metallurgical interface, surface and bulk of the crystal. Nature of defects which cause the degradation and are in turn created is also studied. Dynamics of defects is discussed on effects to reduce the activation energy to break the lattice, and on the energy release mechanism to the lattice. The idea of new Photo-Mechanical Effect, or Recombination Enhancement Effect of defect-formation, -motion, and -annealing is introduced, as a recently clarified mechanism. Accelerated aging data of various devices at various temperatures are shown. There remain things to be done to improve the reliability of “recombination-based” devices which short-live compared with “transport” devices. Understanding of the fundamentals in the degradation processes is the key to the future improvements of these devices.
As the stability of frequency standards have been improved, it becomes desirable to have less noise in the measurement system than the composite noise in the pair of standards to be measured. This paper describes the system and the way of improving frequency stability measurements in the time domain, using the beat frequency method for τ<10s and the phase comparison method for τ<10s. (τ is the averaging time of the measurement.) With regard to the beat frequency method, it became clear that the trigger error of the counter is an important factor for the precision of measurement, and that, in order to make the influence small, the multiplication of the signal frequency is effective. Using a phase meter with a voltage-frequency converter, a frequency stability of 1.0×10-14 was obtained, which corresponds to the noise of this measurement system at an averaging time of 100s.
The ESR measurement of oxygen adsorbed on SnO2 revealed that adsorption of oxygen resulted in the formation of three paramagnetic centers and one diamagnetic center. These centers may be attributed to O2- (g1=2.002, g2=2.009, g3=2.026 and 2.035), O- (g1=2.0015, g2=2.028, g3=2.030), neutral-O2 (g1=1.993, g2=2.003, g2=2.023) and O2- (diamagnetic) respectively. Only the O2- species appeared at the early stage of adsorption at room temper-ature and then it dissociated into the O2- species. Neutral-O2 Species always coexisted with the O2- species and was easily desorbed by evacuation at room temperature. Although the O- species appeared between room temperature and 200°C its adsorption amount was much less than that of the O2- species. The relative amount of adsorbed oxygen species was dis-cussed in connection with the relation between the fermi level and the lowest empty energy level of the adsorbed species.
The measurement of the adsorption isotherm of water-vapour on powdery adsorbents is generally neither precise nor accurate on account of the irreproducibility in the pressure measurements. Sources of the irrepro ducibility are experimentally examined and found to lie mainly in the manometer-oil and in the silicone-grease of the stopcocks. These two materials have proved to absorb or desorb water-vapour depending on its pressure. Therefore, the adsorption measurements through the conventional method where no regard is paid to such phenomena have invariably shown serious deviations. In order to eliminate such disturbing influences, the authors have adopted a kind of blank test. And, moreover, each process of the adsorption measurement is reviewed in view of the multiple system of indirect measurements to propose the optimum conditions for obtaining the adsorption isotherm with a higher precision and a higher accuracy, say ±2%.