Holographic photoelectrochemical etching of diffraction gratings in n-InP and n-GaInAsP for distributed feedback lasers

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Abstract
Direct photoelectrochemical (PEC) etching of diffraction gratings on n‐InP and n‐GaInAsP in a 2‐M HF/0.5‐M KOH solution has been demonstrated using laser interference holography. Development of a maskless technique for producing gratings has potential application in the fabrication of distributed feedback lasers which are currently made by a multistep photoresist process. Submicron diffraction gratings having a period of 0.5 μm, corresponding to second‐order feedback in GaInAsP at λ=1.55 μm, have been achieved. Measurements were obtained on the exposure characteristics, diffraction efficiency, and PEC etching sensitivity of gratings produced in InP and GaInAsP as a function of the writing beam intensity, laser wavelength, material doping level, and grating spatial frequency. For grating frequencies greater than 100 mm−1 the sensitivity was observed to decrease approximately as the inverse square of the spatial frequency. In addition, undoped InP and GaInAsP exhibited significantly lower sensitivities than n‐doped material.