Interpretation of surface phenomena on ZnO by the compensation model

Abstract

Field effect mobility and surface photoconductivity on ZnO crystals increase for several orders of magnitude with dark surface conductivity (electron accumulation). An explanation was given previously: Only a small increasing fraction of the injected electrons appears in the conduction band whereas the main part is trapped by surface states. In the new compensation model the trapping action of the surface states is replaced by that of bulk defects changing their condition of charge within an accumulation layer during variations of band bending: From the temperature dependence of con ductivity and Hall effect a set of three bulk defect levels is evaluated. The same set is used for a newcalculation of the accumulation layer and for a quantitative interpretation of photoconductivity and field effect measurements. Also surface photovoltage and photolysis data are discussed. All these experimental results are obtained on single crystals bearing an accumulation layer. Properties of thin polycrystalline ZnO films are also treated. The concept of a drift mobility is of central importance for the compensation model. As a result of compensation space charge layers are much thinner than previously assumed.

Properties of Indium-Doped ZnO Films Prepared in an Oxygen-Rich Plasma

“…This phenomenon is thought to be ascribed to the number of O Zn defects, which is different from other papers on the photoconductivity of ZnO films or ZnO nanostructure. [15][16][17][18] These papers showed that the persistent photoconductivity had some relation to the oxygen defects or surface states in general. However, the phenomenon was not observed in our samples at 200°C or 400°C substrate temperature, so the surface state effects might seem negligible in the ZnO:In films prepared in the O-rich plasma.…”

Adsorbed Oxygen Ions and Oxygen Vacancies: Their Concentration and Distribution in Metal Oxide Chemical Sensors and Influencing Role in Sensitivity and Sensing Mechanisms

“…Thus, it is vital to characterize oxygen stoichiometry on the surface. Chemical sensor researchers mainly collect the required analytical-spectral-microscopic tools, employing the techniques given in the succeeding paragraphs and detailed in Table 1 [ 21 , 26 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 ]. The full names of each technique detailed in Table 1 is given in the in Abbreviations section at the end of the paper.…”

Análise teórica da interação de CO, CO2 e NH3 com ZnO

“…O óxido de zinco tem sido alvo de inúmeras pesquisas no decorrer dos últimos anos 1,2 com uma importante aplicação em materiais eletrônicos, tais como, células foto-voltaicas 1 , varistores 2,3 , além da grande diversidade de aplicações relacionadas a defeitos 4,5 , catálise [6][7][8][9][10][11][12] , sensores de gases 13 e quimissorção 14 . Superfícies de óxidos são sistemas de especial importância em ciências dos materiais 15,16 , dentre as quais, a superfície do ZnO tem uma diversificada atividade catalítica para um grande número de reações.…”