Abstract
InGaAs-based bow-tie diodes for the terahertz (THz) range are found to be well suited for development of compact THz imaging systems. To further optimize design for sensitive and broadband THz detection, one of the major challenges remains: to understand the noise origin, influence of growth conditions and role of defects for device operation. We present a detailed study of photoreflectance, low-frequency noise characteristics and THz sensitivity of InGaAs bow-tie diodes. The diodes are fabricated from InGaAs wafers grown by molecular beam epitaxy (MBE) on semi-insulating InP substrate under different technological conditions. Photoreflectance spectra indicated the presence of strong built-in electric fields reaching up to 49 kV/cm. It was demonstrated that the spectral density of voltage fluctuations at room temperature was found to be proportional to 1/f, while at lower temperatures, 77–200 K, Lorentzian-type spectra dominate due to random telegraph signals caused by individual capture defects. Furthermore, varying bias voltage, we considered optimal conditions for device room temperature operation in the THz range with respect to signal-to-noise ratio. The THz detectors grown with beam equivalent pressure In/Ga ratio equal to 2.04 exhibit the minimal level of the low-frequency noise, while InGaAs layers grown with beam equivalent pressure In/Ga ratio equal to 2.06 are found to be well suited for fabrication of room temperature bow-tie THz detectors enabling sensitivity of 13 V/W and noise equivalent power (NEP) of 200 pW/√Hz at 0.6 THz due to strong built-in electric field effects.
Highlights
The InGaAs/InP material system is one of the key compounds for ultrafast optoelectronics applications [1]
Despite the fact that InGaAs bow-tie diode displays the advantages of broadband room temperature operation, rather uncomplicated fabrication process and good reliability, its noise equivalent power (NEP) values need to be improved in comparison, for instance, to those of field effect transistors fabricated using
It was demonstrated that the spectral density of voltage fluctuations at room temperature is found to be proportional to 1/f, while at lower temperatures, 77–200 K, Lorentzian-type spectra dominate due to random telegraph signals caused by individual capture defects
Summary
The InGaAs/InP material system is one of the key compounds for ultrafast optoelectronics applications [1]. Despite the fact that InGaAs bow-tie diode displays the advantages of broadband room temperature operation, rather uncomplicated fabrication process and good reliability, its NEP values need to be improved in comparison, for instance, to those of field effect transistors fabricated using. Preliminary investigation has shown that the spectral density of current fluctuations in bow-tie diodes changes with frequency approximately as 1/f and allows us to predict that the origin of noise is a superposition of the capture and emission of charge carriers in defects of the structure [24]. The presented results demonstrate how InGaAs layers grown at different beam equivalent pressure (BEP) In/Ga ratios affect the low-frequency noise level and the sensitivity of the THz detectors. We underline that THz detectors grown with BEP In/Ga ratio equal to 2.06 are found to be most sensitive at room temperature
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