Electric Conductivity and Hall Effect in Evaporated Cadmium Selenide Films

Abstract

Conductivity and Hall effect were investigated on evaporated CdSe films either nontreated or annealed a t 400 and 700 "C. The measurements are performed in the temperature range from -150 to 400 "C. I n the lower temperature range the mobility of electrons follows an exponential temperature dependence of the form peff = po exp ( -A E / k T ) typical for polycrystalline films, which is not only determined by scattering mechanisms alone but also by the numbers and properties of potential barriers a t the crystallite boundaries. These properties of polycrystalline film structure also explain the dependence of conductivity and mobility on film thickness found in non-treated CdSe films. I n the high temperature range conductivity and electron concentrat,ion strongly increase, indicating a self-activated conductivity mechanism. The conduction electron concentration is determined here by thermal intrinsic disorder of lattice atoms.An unbehandelten und bei 400 und 700 "C getemperten CdSe-Aufdampfschichten wurden die Leitfahigkeit und der Halleffekt im Temperaturbereich von -150 bis 400 "C untersucht. I m niederen Temperaturbereich genugt die Beweglichkeit der Elektronen einer fur polykristalline Schichten typischen exponentiellen Temperaturabhangigkeit der Form peff = ,uo exp ( -A E / k T ) , die nicht nur diirch Streumechanismen allein, sondern auch durch die Zahl und die Eigenschaften der Potentialbarrieren an den Kristallitgrenzen bestimmt wird. Diese Eigenschaften der polykristallinen Schichtstruktur erklaren auch die a n nnbehandelten CdSe-Schichten gefundene Schichtdickenabhangigkeit der Leitfahigkeit und Beweglichkeit. I m Hochtemperaturbereich nehmen Leitfahigkeit und Elektronenkonzentration stark zu, was auf einen Eigenstorstellenleitungsmechanisnius hindeutet. Die Leitungselektronenkonzentration wird hier durch die thermodynamische Eigenfehlordnung der Gitterbausteine bestimmt.

Structural and electrical properties of thermally evaporated cobalt phthalocyanine (CoPc) thin films

“…Figures 2a and 2b show the dependence of the planner electrical resistivity, ρ of CoPc films (as-deposited and annealed respectively) for film thickness, d, at different temperatures. As illustrated the resistivity decreases with increasing film thickness in accordance with the results for inorganic [31] semiconductor films and organic films [32]. The behaviour indicates that the electrical resistivity exhibits size effect phenomena in CoPc films.…”

Van der Pauw Resistivity Measurements on Thermally Evaporated Copper Phthalocyanine Thin Films

“…Below 1.0 pm thickness the resistivity decreased with increasing film thickness in accordance with typical results for inorganic semiconducting films [3], and becomes almost constant, exhibiting a value of about 2 x lo8 Q m. A similar thickness dependence of dark current has been reported by other workers on planar lead phthalocyanine samples for thicknesses in the range 50 to 400 nm [4]. It was ascribed to an increase in mobility due to increasing crystallite size with film thickness in the case of inorganic materials [3].…”

Electrical Transport Properties of Thermally Evaporated Phthalocyanine (H2Pc) Thin Films

“…The change in the slope and hence the activation energy is interpreted as a change from extrinsic to intrinsic conduction [12]. The value of the thermal activation energy ∆E 1 is nearly 0.156 ± 0.019 eV and ∆E 2 is nearly 0.766 ± 0.12 eV, which is in good agreement with those obtained by other workers [3][4][5][6][7][8][9][10][11][12][13][14][15]. The temperature dependence of the resistivity for annealed films is shown in Fig.…”

“…As illustrated, the resisitivity decreases with increasing film thickness i.e. follows the known behaviour of organic and inorganic semiconductors [9,10]. Figure 1b shows the dependence of the resistivity, ρ, (for annealed films at 623 K for one hour) on film thickness at different temperatures.…”