Germanium, electrodeposition

Fig. 4.2 Weight (including Archimedean force) of the cathode with the deposit vs. time in course of germanium electrodeposition from KF-NaF-K2GeFs-Ge02 melts at 750 °C in galvanostatic conditions. Dashed straight line corresponds to the deposition of pure germanium with 100 % Faradaic efficiency [8]. The numbers indicate the ratio of Ge02 to K2GeFs in the electrolyte...

Germanium In situ STM studies on Ge electrodeposition on gold from an ionic liquid have quite recently been started at our institute [59, 60]. In these studies we used dry [BMIM][PF<3] as a solvent and dissolved Gel4 at estimated concentrations of 0.1-1 mmol 1 the substrate being Au(lll). This ionic liquid has, in its dry state, an electrochemical window of a little more than 4 V on gold, and the bulk deposition of Ge started several hundreds of mV positive from the solvent decomposition. Furthermore, distinct underpotential phenomena were observed. Some insight into the nanoscale processes at the electrode surface is given in Section 6.2.2.3. 

Figure 6.2-12 Cyclic voltammogram of 0.1 - 1 mmol dm Geb on gold in dry [BMIMj PFg , starting at-500 mV towards cathodic (a) and anodic (b) regime. Two quasireversible (E, and E2) and two apparently irreversible (E4 and E5) diffusion-controlled processes are observed. E3 is correlated with the growth of two-dimensional islands on the surface, E4 and E5 with the electrodeposition of germanium, Ej with gold step oxidation, and E, probably with the iodine/iodide couple. Surface area 0.5 cm (picture from [59] - with permission of the Peep owner societes).

Semiconductors (cont.) equilibrium in. 1076 exponential law, 1081 germanium as, properties, 1076 hole movement 1076 impedance of, 1136 importance of, 785 limiting current 1088 n-, in thermal reactions, 1086 n-pjunction, 1073, 1081 p- in thermal reactions. 1086 photoactivity of, 1089 photoelec trochemistiy, 1073 photos timulated electrodeposition on. 1345 potential variation with distance in, 1082 silicon as, properties, 1076 surface states. 1086 symmetry factor in, 1082 thermal reactions, definition, 1088 Sen, 1495... 

In this chapter we have summarized selected literature data on the electrodeposition of semiconductors in ionic liquids. It has been demonstrated that elemental silicon, germanium, and selenium can be elecrodeposited in ionic liquids. Furthermore, it is shown that compound semiconductors like InSb, AlSb, CdTe and others can be made, especially at elevated temperatures where kinetic barriers are easier to overcome, even allowing the exclusive electrodeposition of grey selenium. In this context ionic liquids are very promising for semiconductor electrodeposition. Both wide electrochemical and thermal windows allow processes which are impossible in aqueous or organic solvents. 

Ge(lll) bilayers can be obtained by electrodeposition in the dry ionic liquid [BMIMJPF6 containing GeT as a source of germanium [94], This ionic liquid has an electrochemical window of a little more than 4 V on Au(lll). However, stable... 

Electrolytic dissolution processes will be discussed here since it is normally very difficult to electrodeposit semiconductors. Results obtained with silver on one hand and with germanium on the other will be presented since these cases are best understood. 

Endres F (2001) Electrodeposition of a thin germanium film on gold from a room temperature ionic liquid. Phys Chem Chem Phys 3 3165-3170... 

Endres F, Abedin SZE (2002) Electrodeposition of stable and narrowly dispersed germanium nanoclusters from an ionic liquid. Chem Commun 2002 892-894... 

Endres F (2002) Electrochem electrodeposition of nanosized germanium from GeBr and GeCl in an ionic liquid. Solid-State Lett 5 C38-C42... 

As a third example of our in situ STM results we would like to draw attention to the electrodeposition of Germanium [69,70,79]. Germanium is an elemental semiconductor with a band gap of 0.68 eV at room temperature in the microcrystaUine phase. Furthermore, in contrast to metals, its crystal stmcture is determined by the tetrahedral symmetry of the Ge atoms, so the diamond stmcture is thermodynamically the most stable one. Germanium can hardly be obtained in aqueous solutions... 

The surface consists of terraces with a height of330 30 pm. Within the limits of error, this is the value that has to be expected for Ge(lll) bilayers. Furthermore, we could observe that the first electrodeposition leads to a less ordered sur ce sttucture with nanoclusters, which transforms on the time scale of about 1 h into a layered structure. With GeBr4 a transformation of clusters into such a layered sur ce was only partly seen, with GeCl4 this transformation could not be observed. The oxidation of the deposited germanium is also a complicated process. We found that mainly chemical oxidation by Gel4 takes place, together with some electrooxidation. It is likely that kinetic factors play a dominant role. 

Figure 6.2-23(a) shows the STM picture of an about 100 nm thick silicon layer that was electrodeposited at —1600 mV vs. Fc/Fc, probed under potential control with the in situ STM. Its surface is smooth on the nanometer scale and its topography is similar to that of a germanium layer of comparable thickness [79]. Figure 6.2-23(b)... 

Andriiko AA, Tchemov RV (1983) Electrodeposition of powdered germanium from oxide-fluoride melts. In Physical chemistry of ionic melts and solid electrolytes. Naukova Dumka, Kiev, pp 46-60... 

Andriiko AA, Tchemov RV (1983) Electrodeposition of powdoed germanium from... 

Such electrodeposition process had been widely investigated for electroreduction of germanium species in molten KF-NaF-K2GeF6-Ge02 electrolyte [8]. One of the most interesting information has been obtained with the automatic balance experimental technique permitting to record the weight of the electrode in situ in course of the electrolysis [9]. 

Fig. 4.3 Kinetics of potentiostatic electrodeposition of germanium from the oxyfluoride melt...

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