Franz-Keldysh effect in lateral GaAs/AIGaAs based npn structures

Lateral npn structures, fabricated by focused laser beam-induced doping, combine large potential modulations with a small width of the p-doped regions. This results in strong lateral electric fields, which can be tuned by applying a bias voltage. Photon absorption for energies below the band gap is allowed due to the Franz-Keldysh effect. We estimate the value of the electric fields by analyzing wavelength-dependent photocurrent measurements. The fields are comparable to attainable fields in existing vertical modulator structures. The spatially resolved photocurrent measurements reveal the location of the highest lateral electric field, which is at the edges of the p -doped region.