Publisher Summary This chapter highlights noise as a measure of quality and reliability in electronic devices The chapter attempts to describe what mechanisms have been well established as a source of noise related to the defective or nonideal nature of electronic devices This chapter is devoted to an account of the success that has been obtained in using noise as a nondestructive indicator of reliability The chapter is mainly concerned with a review of the properties of noise and some of the general principles behind the specific mechanisms Noise arises from many possible defects so that monitoring this single quantity can detect the presence of one or more of many different defects It is, therefore, necessary to be careful in interpreting noise results to ensure that a correct mechanism is assigned to the noise, and even greater care is necessary in comparing noise results among different specimens, because the origins and characteristics of the noises may be completely different As many of the detailed mechanisms for the production of the excess noise are becoming understood, the use of noise as an analysis quantity can increase

Electrical Noise as a Measure of Quality and Reliability in Electronic Devices

We developed a simple but efficient method to mass-produce highly flexible and high-performance photodetectors based on aligned cadmium sulfide (CdS) nanowire (NW) networks. In this method, the CdS NWs were selectively aligned along the molecular patterns on flexible substrates via a direct assembly method, and the aligned CdS NW patterns were utilized as the channels of flexible photodetectors. The photodetectors based on the aligned CdS NWs exhibited ∼10 times higher photosensitivity and ∼100 times faster photoresponse than those based on randomly oriented NW networks. In addition, the flexible photodetectors exhibited stable photoconductive characteristics even when these were bent down to the radius of curvature of 0.2 mm. This research may pave the way for the large-scale fabrication of low-cost and high performance flexible photodetectors based on the aligned NW networks.

Aligned networks of cadmium sulfide nanowires for highly flexible photodetectors with improved photoconductive responses

The model of electroluminescence in forward-biased MS and MIS light-emitting diodes based on the Auger recombination on the contact surface of the semiconductor is developed. Such a model may provide a light emission with the threshold voltage Uth = (Eg/2e) – (Efs/2e) < hνmax/e or even Uth = (hνmax/2e) – (Efs/e), depending on the physical processes involved. Here Eg, is the energy gap of the semiconductor, Efs the Fermi energy level in the semiconductor with respect to the c-band edge, hνmax the maximum of the electroluminescence band, e the electron charge. Experimental results obtained on ZnS MS and MIS diodes essential for this model are presented and analysed. It is found that the spectral distribution of diode emission remains practically unchanged at biases close to the threshold voltage Uth. The conclusion is drawn that the electroluminescence and the forward current have typical tunnel characteristics even in the case of ZnS MIS diodes with i-layers several thousand angstroms thick. The main physical properties of zinc chalcogenide light-emitting diodes are explained by means of the model developed.



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Mechanism of electroluminescence excitation in forward‐biased MS and MIS light‐emitting diodes based on wide‐band‐gap II–VI compounds

Low frequency noise as a tool to study optocouplers with phototransistors

NMR measurements of Cu and Cl nuclei are carried out at 1.75 K to clarify the distribution of Cl - and Br - ions in the slowly grown mixed crystals (CH 3 NH 3 ) 2 Cu(Cl 1- x Br x ) 4 from an aqueous solution. The analysis of the Cu NMR spectra reveals that the Cl - and Br - ions do not distiribute at random. By comparing the NMR intensities of Cl nuclei on the c -axis with those in the c -plane, it is concluded that most of Cl - ions preferentially occupy the positions in the c -plane.

Distribution of Cl − and Br − Ions in Mixed Crystals (CH 3 NH 3 ) 2 Cu(Cl 1− x Br x ) 4

The excess fluctuations of the direct current and of the forward-bias electroluminescence intensity in GaAs-diodes have been investigated. The diodes of two types have been studied: the samples doped by non-amphoteric impurities (type I diodes) and the samples doped by non-amphoteric together with amphoteric impurities (type II diodes). The current noise in type I samples as well as in the wide current range in type II samples is shown to be generated in the space charge region of diodes. These noises are as a matter of fact the fluctuations of the excess component of the whole current which is likely to pass through some ‘peculiar’ regions of p - n -junctions rather than through the whole area. The current noise observed in type II diodes at sufficiently large currents is due to the fluctuations of the resistance of the compensation region of the diode or due to the fluctuations of its contact resistance. The excess electroluminescence noise in all diodes investigated has been found to be connected with the above-mentioned fluctuations of the excess component of the whole current and in the type II samples the over-barrier electron flow responsible for the electroluminescence passing probably through the same ‘peculiar’ regions of p - n -junction as the excess current does.

Nature of current and of forward-bias electroluminescence excess noise in GaAs-diodes

Excess current and luminescence noise of P-N junctions in GaP

The results of simultaneous investigations of noise characteristics and contact resistance of different contacts to low-resistivity ( ρ b = 1–10 ohm cm) ZnS single crystals including so-called ohmic contacts with a contact resistance ρ c = 0.1–0.5 ohm cm 2 are described and analyzed. A conclusion is drawn that the difficulties in obtaining ohmic contacts to low-resistivity ZnS are connected with the presence on the semiconductor contact surface of acceptor centers filled by electrons which are responsible for the increase of band bending at the semiconductor surface. In the case of ohmic contacts the contact barrier is lowered significantly owing to formation of the ionized donor centers in the contact region; electrons penetrate such barriers by tunneling.

Ohmic contacts to low-resistivity ZnS: Preparation, noise properties and nature of contact resistance

Peculiarities of the photocurrent noise and of the residual (“frozen”) conductivity are analyzed theoretically for the model of a CdS-type photoconductor. The significant element of this model is the existence of the collective recombination barrier. It is shown that in the cases where such a model is realized, the appearance of 1 ƒ portions in photocurrent noise spectra as well as in the noise spectra of the residual conductivity should be expected. Experiments are proposed and carried out which confirm the existence of the connection between the occurence of 1 ƒ portions in the noise spectra and the presence of the collective recombination barriers. Thus, the nature of the high-frequency 1 ƒ portions which have been often observed in photocurrent noise spectra of CdS is established. These have been erroneously ascribed to peculiarities of exchange between the c-band and the traps. The direct experimental proof of the dominating role of the recombination barriers in the residual conductivity phenomena is obtained.

M.K. Sheinkman

Papers

Nature of current and of forward-bias electroluminescence excess noise in GaAs-diodes

Excess current and luminescence noise of P-N junctions in GaP

Ohmic contacts to low-resistivity ZnS: Preparation, noise properties and nature of contact resistance

High-frequency 1ƒ noise of photocurrent and residual conductivity in CdS