AlGaAs emitter∕GaAs barrier terahertz detector with a 2.3 THz threshold

Abstract

A heterojunction interfacial work function internal photoemission ͑HEIWIP͒ detector with a threshold frequency ͑f 0 ͒ of 2.3 THz ͑ 0 = 128 m͒ is demonstrated. The threshold limit of ϳ3.3 THz ͑92 µm͒ due to the Al fraction being limited to ϳ0.005, in order to avoid control and transition from alloy to isoelectronic doping behavior, was surpassed using AlGaAs emitters and GaAs barriers. The peak values of responsivity, quantum efficiency, and the specific detectivity at 9.6 THz and 4.8 K for a bias field of 2.0 kV/ cm are 7.3 A / W, 29%, 5.3ϫ 10 11 Jones, respectively. The background-limited infrared photodetector temperature of 20 K with a 60°field of view was observed for a bias field of 0.15 kV/ cm. The f 0 could be further reduced toward ϳ1 THz regime ͑ϳ300 m͒ by adjusting the Al fraction to offset the effect of residual doping, and/or lowering the residual doping in the barrier, effectively lowering the band bending.

Wavelength and polarization selective multi-band tunnelling quantum dot detectors

“…For In 0.6 Ga 0. 4 As dots in Al 0.3 Ga 0.7 As with 13-nm diameter and 6-nm height, the ground and first excited states in the x and z -directions are 154 (E 0 ), 241 (E 1 ), and 410 meV (E 2 ) above the conduction band of the dot. Even though there are additional excited states in the dot, they do not contribute to the photocurrent.…”

“…One of the challenges in developing terahertz detectors is the reduction of the dark current (due to thermal excitations) associated with terahertz detection mechanisms. At the present time, terahertz detectors such as Ge BIB detectors [1], photo conductors triggered by femtosecond laser pulses [2], quantum well detectors [3], hetero junction detectors [4], and thermal detectors, such as bolometers and pyroelectrics all of which operate at low temperatures, are being studied. A typical detector structure, in which the transitions leading to terahertz detection occur between two electronic states with an energy difference of DE (4.1 meV for 1 THz), would not be suitable for high temperature terahertz detection since the thermal excitations become dominant even at 77 K due to small DE.…”

Dopant Migration-Induced Interface Dipole Effect in n-Doped GaAs/AlGaAs Terahertz Detectors

“…The Al fraction in the above structure was determined by XRD measurements and numerical fittings. In case of p-type HEIWIP [2], no dopant migration was observed in the reported detectors since there is no possibility of formation of an interface dipole between interface states and ionized acceptor atoms because of their identical charge polarity. Note that the dipole effect is not observed in multiple quantum well devices due to the δ doping method, which cannot be used for free carrier absorption-based detectors.…”

“…The competitive approaches for THz detection include homojunction [1] and heterojunction interfacial workfunction internal photoemission (HEIWIP) [2] THz detectors in which the basic detection mechanism is the free carrier absorption in an emitter region and the collection of the photoexcited carriers over an undoped barrier. Most HEIWIP detectors [2] reported are p-type doped emitters. Faster response speed due to low effective carrier mass in n-type HEIWIP detectors may be of interests for high-speed applications.…”

Terahertz Detection with δ-Doped GaAs/AlAs Multiple Quantum Wells

“…Quantum structures, fabricated by molecular beam epitaxy (MBE), are an attractive choice as they allow, depending on the precise structure design, different physical mechanisms to be used for the emission/detection of THz radiation. An excellent example of a compact emitter is the THz quantum cascade laser [1], whilst in detection, THz quantum well infrared detectors (QWIPs) [2] or heterojunction interfacial work function internal pho-toemission detectors (HEIWIPs) [3]) are being developed. These devices exploit vertical carrier transport which can be engineered by varying the widths of the wells/barriers and the doping profile.…”