Investigation of porous Si, formed by metal-assisted chemical etching with Au as catalyst

Straight pores formed in silicon (Si) have attracted attention for their applications in various fields such as membranes, photo- and betavoltaics devices, bio- and chemical sensors and many others. Metal-assisted etching... [ view full abstract ]

Straight pores formed in silicon (Si) have attracted attention for their applications in various fields such as membranes, photo- and betavoltaics devices, bio- and chemical sensors and many others. Metal-assisted etching (MACE) has been studied as a novel method for production of a porous structure in Si. Metal films or particles loaded on Si wafers are used as catalysts for etching of Si in aqueous solutions of HF and H2O2 without external electrical power.
This abstract describes a method of porous layers formation using no continuous gold film as a catalyst in the aqueous solution of HF and H2O2 during 10, 30 and 50 minutes. The solution temperature was in the range of 25 °C to 70 °C. Initial substrate was p-(100) type Si with resistivity 0,01 Ohm•cm. In the work were calculated growth rate of the porous layer thickness (Vh) and pore diameter (Vd) at various temperatures solution. The plot of 1/Т vs. lnVh and lnVd showed a good straight in the range of 25 ˚C to 70˚C (Fig.1). The growth rate of the porous layer thickness is described by the following equation: Vh=2,6•10^10•exp (-0,54/kT), where Eah=0,54 eV - the activation energy of growth, A1=2,6•10^10 nm/min is pre-exponential factor at Eah. The increase rate of the pore diameter is described by the following equation: Vd=1,01•10^12•exp (-0,66/kT), where Ead=0,66 eV, А2 =1,01•10^12 nm/min at Ead. Accordingly, an activation energy (Ea) and pre-exponential factor (A) were calculated, using the Arrhenius equation.
The etching rate of single-crystal silicon increases due to the increase of chemical reaction rate with temperature. Moreover the temperature increase is lead to reducing the hole-injection barrier between the Au and Si and carrier injection into semiconductor. It leads to growth of total hole current.

Figure 1 - Arrhenius plot of the growth rate of the porous layer thickness (Vh) and pore diameter (Vd) versus reciprocal temperatures solution.

The reported study was funded by RFBR according to the research project No 16-33-00712 мол_a.