The paper investigates a model of the photoconductivity of macroporous silicon in the conditions of homogeneous generation of photocarriers. By the finite element method, the stationary photoconductivity and the time evolution of photoconductivity after instantaneous shutdown of light are calculated. Dependences of the stationary photoconductivity and relaxation time of photoconductivity on the velocity of recombination of nonequilibrium carriers at the surfaces of pores, radius of pores, and average distance between them are analyzed.

One of urgent today’s problems is the control of toxic and other harmful substances in air atmosphere, drinking water, foods, and so forth. In this connection, there is a necessity for development of microelectronic systems of detection of gases for industrial, office, and housing apartments which can be components of integral systems of protection of human’s life and health. Of special interest is the sensors based on nanoporous semiconductors, in particular porous silicon. Gas sensors of such type are described in a number of papers [

In this paper, for the case of macroporous silicon with cylindrical pores, modeling of stationary photoconductivity and process of its relaxation occurring after instantaneous shutdown of illumination is carried out.

Let us consider a plate of macroporous silicon with arranged parallel cylindrical pores of radius

The generated photocarriers recombine both in the semiconductor volume and at the surfaces of pores. At constant illumination, it has been established such a nonuniform spatial distribution of photocarrier concentration at which balance between the processes of generation and recombination of nonequilibrium charge carriers is ensured.

In the case of diffusion transport of photocarriers, the dependence of the photocarrier concentration

Equation (

The initial condition for (

The total number of photocarriers

For convenience, we further pass to the following dimensionless values:

In the stationary case, the left-hand side of (

Dependences of total number of photocarriers on

It is seen from Figure

Along with the numerical modeling, we have carried out analytical calculation for the case of cylindrical symmetry of the problem which takes place when

Comparison of the results of numerical and analytical calculations shows that, at

We shall analyze the nonstationary photoconductivity for the case of instantaneous shutdown of light falling on the semiconductor plate, that is, when the function

The total number of photocarriers

The calculated dependences

Dependences of photoconductivity relaxation time on

In this paper, we have calculated by the finite element method the stationary photoconductivity and the time of photoconductivity relaxation for the case of macroporous silicon with cylindrical pores. It has been shown that both stationary photoconductivity and time of photoconductivity relaxation significantly depend on the surface recombination velocity of photocarriers, radius of pores, and average distance between pores what can be used for manufacturing gas sensors. Photoconductivity of macroporous silicon at fixed nonzero value of the velocity of surface recombination decreases with increasing the pore’s radius and increases with rising the average distance between them. Photoconductivity relaxation time nonlinearly decreases with increasing the velocity of surface recombination, and the most significant decrease of relaxation time takes place when value of the velocity of surface recombination is of the order of one.