Comparative Study of the Photoelastic Anisotropy of Si and GaAs

In this paper we present the results of experiments on single-crystalline (100)Si and (100)GaAs wafers which allow us to determine the degree of photoelastic anisotropy Ape in the near-infrared range (probing laser wavelength λ ≈ 1.3 μm). Ape is introduced as the absolute value of (π11 − π12 − π44)/(π11 − π12 + π44). π11, π12 and π44 are the piezo-optical coefficients. The experiments were carried out using a scanning infrared depolarization imager (SIRD) measurement system equipped with special calibration setups. These setups produce a defined diametrical loading of the wafer. The different measurement and analysis strategies are explicated. The generated birefringence and shear stress equivalent maps impressively illustrate the respective opposite photoelastic properties of Si and GaAs. The experimental results are compared with simulation data on the basis of a classic 2D stress model, taking into account the crystallographic anisotropy by applying the full tensor calculus. For GaAs, Ape is determined to be 0.41 ± 0.02. This value and the best-matching coefficients πij which were used for simulation are compared with data available from publications of the past few decades.