Photocurrent oscillation

FIGURE 5.50. The amplitude of the photocurrent oscillations on illuminated n-Si as a function of the applied potential in 0.1 M NH4F at pH 4.0, light intensity 70mWcm". (Reprinted from Aggour et at 1990, with permission from Elsevier Science.)... 

During the oscillation the thickness of the oxide film on the silicon surface varies periodically, the frequency of which coincides with the associated current oscillation. Figure 5.55, for example, shows the variation of oxide thickness, about 2 nm in amplitude (or about 25% of the average thickness), during the photocurrent oscillation of n-type silicon at TVs e in a solution of 0.1 M [F and pH 4.4. ° The anodic current is... 

M. Aggour, M. Giersig, and H. J. Lewerenz, Interface condition of n-Si(lll) during photocurrent oscillations in NH4F solutions, J. Electroanal. Chem. 383, 67, 1995. 

Figure 2.54 Photocurrent oscillations for n-Si(lll) at 4 = -r6V in 0.1 M NH F, pH 4 (top) and oxide thickness variation determined by in situ Fourier transform...

Figure 2.85 Pore deepening protocol (current versus time) for an oxide matrix prepared by photocurrent oscillations after sample emersion at the increasing branch of the oscillatory current solution, 4M NaOH potential held at-0.85V (SCE).

A thorough insight into the comparative photoelectrochemical-photocorrosion behavior of CdX crystals has been motivated by the study of an unusual phenomenon consisting of oscillation of photocurrent with a period of about 1 Hz, which was observed at an n-type CdTe semiconductor electrode in a cesium sulfide solution [83], The oscillating behavior lasted for about 2 h and could be explained by the existence of a Te layer of variable width. The dependence of the oscillation features on potential, temperature, and light intensity was reported. Most striking was the non-linear behavior of the system as a function of light intensity. A comparison of CdTe to other related systems (CdS, CdSe) and solution compositions was performed. 

Fig. 24. Potentiodynamic polarization curve of Cu in 0.1 M KOH with anodic and cathodic current peaks and the related reactions of oxide formation or reduction dissolution of cations and the indication of the stability ranges of the CU2O and duplex oxide layer, z ph at CII indicates oscillating photocurrent due to a chopped light beam [86],...

In photocathode electron guns, the timing between the microwaves used for acceleration and the photocurrent-generating laser pulse is of critical importance. Precise synchronization between the laser and electron beams is obtained by using a MHz quartz master oscillator to control the cathode pump laser repetition rate and the microwave amplifier system seed frequency (Fig. 3). 

The spectrum of lattice-trapped atoms is recorded using a heterodyne technique. Light fluoresced by the trapped atoms is combined with light (frequency shifted by a modulator) from the laser forming the lattice. When the beams mix on a photodiode they create a beat signal at the difference frequency between the fluorescence and the frequency-shifted laser. The power spectrum of the photocurrent is identical to the fluorescence power spectrum, but centered at radio frequency. This heterodyne technique is not sensitive to the frequency jitter of the laser because the jitter is common between the fluorescence and the laser, which acts as a local oscillator. 

The photocurrent (n-Si) and dark current (p-Si) oscillations, described in Section 2.4.1, result in nanoporous oxide films as can be seen in Figure 2.55. Those pores that are deep enough to reach the underlying Si have electrical contact and... 

If a narrow spectral feature is present with linewidth on the order of or less than 03m, the unbalancing of the two sidebands will convert the phase-modulated laser beam into an amplitude-modulated beam which produces a strong oscillating photocurrent at cUm at the detector output. More precisely, the detected signal at the I port of the mixer (in the absorption phase) is proportional to [a(cOc -I- com) - a(wc - (Om)]L where a is the absorption coefficient and L is the sample thickness. Thus the FM signal measures the difference in aL at the two sideband frequencies. For a spectral feature narrower than tUm, two copies of the absorption line appear, one positive and one negative, as each of the two sidebands is swept over the absorption. 

Applying the boundary conditions Eqs (48) and (49), the electron transport Eq. (47), can be solved in the frequency domain and the harmonic photocurrent, driven by the harmonic oscillation of the irradiation intensity, reads... 

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