Abstract

A GaAs Nipi with selective contacts was used for refractive modulation characterization; this Nipi device has the alternative n- and p-doped thin layers at a total thickness of ≅ 0.68 μm and a doping concentration of n ≅ p ≅ 4×10¹⁸ cm^-3. The selective contactings were grown in situ with the n-i-p-i structure by MBE technology. The distance between two contact electrodes is ≅ 0.7 mm and each electrode is measured at ≅ 1 mm in length. The active area of this device is, therefore, approximately 0.7 mm × 1 mm. The I-V measurement of this n-i-p-i device shows good diode characteristics. The refractive changes at various current levels were determined by using a Mach-Zehnder interferometer. An Ar⁺-laser pumped ring dye laser, which has a useful wavelength range from 8000 to 9000 Å, was used as a light source. The refractive index change was determined by the fringe shift of the interference pattern generated by the signal beam (which passes through the n-i-p-i device) and the reference beam. A train of current pulses at a few hertz was used to drive the n-i-p-i modulator and also eliminate the slow fringe drift due to environmental noises of the interferometric system. A positive refractive index change of Δn > 1.5 was recorded at an injection current level I < 50 mA at λ = 9000 Å, as shown in Figure 1. The above result of refractive index modulation is more than two orders of magnitude larger than the prediction from our theoretical calculation.¹ This refractive index change is observed in the wavelength range from 8900 Å to 9050 Å. The measurement wavelength range was limited by the strong interband absorption at λ < 8900 Å, and by the cutoff lasing wavelength of the sty-9 dye used in our ring dye laser beyond λ > 9050 Å.

© 1989 Optical Society of America