InGaAs Diodes for Terahertz Sensing—Effect of Molecular Beam Epitaxy Growth Conditions

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.

Roadmap of Terahertz Imaging 2021

“…They were found to be well-suited for multispectral THz imaging aims [178,179], and, together with their reliability and fast response times below 7 ns [180], can be implemented in real imaging systems to discriminate even weakly absorbing objects when tuned to heterodyne [181] or homodyne [182] operational modes. Recent technological innovation making use of new growth conditions [183] enabled increase of the sensitivity of 13 V/W and reduction of the NEP below 1 nW/ √ Hz at 0.6 THz due to strong built-in electric field effects.…”

Low-Frequency Noise Investigation of 1.09 μm GaAsBi Laser Diodes

“…When the temperatures are below 250 K (Figure 11a) the relaxation time τ = 1/(2π f 0 ) is dependent on temperature and is described as: τ=τ0expfalse(Ea/kTfalse) [17], where E a is the activation energy of an observed g-r process. The maximum ( S U / U 2 ) f value appears when the Fermi level coincides with the trap energy level [13,28]. At temperatures T > 250 K the relaxation time is almost independent of temperature showing that the Fermi level is bound to the accumulation of defect levels in a particular place of the bandgap of the LD active region (Figure 11b).…”

Responsivity and NEP Improvement of Terahertz Microbolometer by High-Impedance Antenna

“…Another class of the THz detector is the detector based on the rectification by electron devices with nonlinear characteristics. Field-effect transistors [ 25 , 26 ], diodes [ 27 , 28 ], and high electron mobility transistors [ 29 , 30 ] are among the most studied rectifying devices for THz detection. They are fast, allow for room temperature operation, and facilitate direct or heterodyne detection of THz signals.…”