We apply computer algebra method to solve the problems arising in physics of semiconductor devices. We used a theory for interband tunneling (V. Ryzhii and A. Zhakharova, Semicond. Sci. Technol. 8 (1993), 377-382) to solve the Schroedinger equation for multi layer broken-gap heterostructures. This yields a method to obtain an error estimate for the approximate solution of the Schroedinger equation and gives new insight into interband tunneling in semiconductor heterostructures.