固体C_(60)/Si异质结的电学表征——整流特性、能带模型与温偏效应

ELECTRICAL CHARACTERIZATION OF SOLID C60/Si HETEROJUNCTIONS RECTIFYING PROPERTIES, ENERGY-BAND MODELS, AND BIAS-TEMPERATURE EFFECT

研究了非掺杂固体C_(60)与n-Si和与p-Si接触的电学性质,电流-电压(J-V)特性测量表明两种接触的导电极性相反,且都具有很强的整流作用,表明在两种接触界面附近存在着阻挡载流子输运的、性质不同的势垒.电流-温度(J-T)测量表明,电流与温度的倒数呈指数依赖关系,从中估算出C_(60)/n-Si和C_(60)/p-Si异质结的有效势垒高度分别为0.30和0.48eV.引进异质结的能带模型,成功地解释了上述测量结果,由能带模型和测量数据估算出以硅为衬底的固体C_(60)膜的电子亲合能为3.92eV,禁带宽度小于1.72eV,高频电容-电压(C-V)测量表明:温偏对异质结的C-V特性有严重影响,用C_(60)膜中的可动负离子效应成功地解释了这一现象,并估算出负离子浓度为3.1×10^(12)cm^(-2).用高频C-V测量准确确定了C_(60)的相对介电常数,在300—370K温度范围内其值为3.7±0.1.

This work investigates electrical properties of contacts between undoped solid C60 and n-or p-type Si. Current-voltage measurements show that the two contacts result in strong rectification with opposite conduction directions, indicating two different kinds of barriers for carrier transportation at the interface of the two contacts. Current-temperature measurements show that the current is an exponential function of reciprocal temperature, from which we estimate the effective barrier height to be 0.30 and 0.48 eV for C60/n-Si and C60/p-Si, respectively. Within energy-band models we interpret successfully the above experimental results. Based on the energy-band model and experimental data we derived the electron affinity of solid C60 film to be 3.92 eV and its energy gap to be below 1.72 eV. Highfrequency capacitance-voltage measurements show that biastemperature treatments have considerable effect on the C-V characteristics of the heterojunction. Assuming the existence of mobile negative charges in the solid C60 film we explain the effect successfully and estimate the density of the negative charges to be 3.1 x 1012 cm-2. By use of the C-V results we determine the dielectric constant of the solid C60 film to be 3.7±0.1 in the temperature range of 300-370 K.