Photochemical etching of n -InP as a function of temperature and illumination

Photochemical (PC) etching of n-InP using an Ar+ laser and dilute phosphoric acid solutions was studied as a function of temperature, power, illumination frequency, and duty cycle. The etch rate was found to be independent of time and to increase fourfold by increasing temperature from 20 to 50 °C with an activation energy ≳0.34 eV. Thus the process is found to be reaction rate limited. The etch rate was observed to increase with power for low-power levels and then saturate near an irradiance of 200 W/cm2 at 20 °C. The photoetch rate, i.e., the etch rate divided by the fraction of time the Ar+ light is on, was affected by illumination duty cycle but not chopping frequency in the range 100–3200 Hz. These results are explained based on a rate equation model for material removal. Finally, a new application for PC etching is presented: sample preparation for transmission electron microscopy.