Terahertz range quantum well infrared photodetector

Abstract

We demonstrated a GaAs/AlGaAs-based far-infrared quantum well infrared photodetector at a wavelength of ϭ84 m. The relevant intersubband transition is slightly diagonal with a dipole matrix element of 3.0 nm. At 10 K, a responsivity of 8.6 mA/W and a detectivity of 5ϫ10 7 cm ͱHz/W have been achieved; and successful detection up to a device temperature of 50 K has been observed. Being designed for zero bias operation, this device profits from a relatively low dark current and a good noise behavior.In recent years, there has been an increasing interest in the fabrication of so-called terahertz ͑THz͒ emitters and detectors. While electronic devices like Gunn diodes or Schottky diode frequency multipliers try to reach this range from the low frequency end, optical devices like gas or semiconductor lasers are quickly moving into the THz range from the high frequency side. [1][2][3] Since the THz region is traditionally defined as 0.1-3 THz, the currently available quantum cascade laser ͑QCL͒ sources with ϭ87 m can already be regarded as THz sources. At low temperatures, they emit several milliwatts of continuous wave output power. On the electronics side, Gunn diodes and frequency mixers have also achieved several milliwatts of radiated power at frequencies on the order of hundreds of gigahertz. 4 Once the entire THz frequency range is fully accessible by convenient radiation sources, it is obvious that the next important step towards applications is the development of suitable detectors. Like any other type of electromagnetic radiation, THz waves or pulses can be detected by coherent or incoherent means. Most coherent detection schemes utilize frequency conversion, whereas incoherent methods are based on the heat production of absorbed radiation. Typical examples of heat detectors include Si-bolometers or pyroelectric crystals like deuterated triglycerine-sulfate ͑DTGS͒; on the other hand, Schottky diode mixers, 5 nonlinear optical crystals like ͕110͖ ZnTe, 6 and gated photoconductive antennas are typical coherent detection schemes. 7 As a further incoherent solution, semiconductor-based quantum-type approaches like biased superlattices have attracted some attention.8 Bolometers are in general highly sensitive, but like all heat-based detection schemes, they are intrinsically slow and built for very low temperature operation only.9 DTGS detectors and pyroelectric crystals offer the advantage of faster detection at the prize of reduced sensitivity. Finally, extrinsic photoconductors such as doped Ge detectors are fast and sensitive, but they must be cooled to 4 K. Quite generally, coherent techniques profit from a good sensitivity, but they are experimentally more sophisticated than incoherent ones.10 Although semiconductor quantum devices might not be highly sensitive, their potential for mass fabrication and integration by means of semiconductor device technology is very appealing. This has been proven by different types of quantum well infrared photodetectors ͑QWIPs͒ which work in a variety of different wavelength...

Designer Multimode Localized Random Lasing in Amorphous Lattices at Terahertz Frequencies

“…Notable achievements include the invention and advancement of THz quantum cascade lasers (QCLs) 19,20 , sensitive THz photodetectors 21,22 , and THz modulators 23,24 . THz QCLs are electrically-pumped semiconductor-based lasers based on electronic transitions between the subbands of a quantum well superlattice 19 .…”

Photoreflectance and surface photovoltage spectroscopy of beryllium-doped GaAs∕AlAs multiple quantum wells

“…The facilities of modern molecularbeam epitaxy ͑MBE͒ technology enable semiconductor quantum wells ͑QWs͒ to be engineered so that the carrier transitions in subbands can be used either to generate THz radiation by a quantum cascade scheme 1 or to detect THz frequencies, for instance, employing quantum well infrared photodetector ͑QWIP͒ approach. 2 The other way to proceed, which attracts much attention due to easier fabrication and lower costs, is to involve impurities in bulk semiconductors since their transitions also fall into THz frequency range. As an illustration of such a kind of detection it is worth mentioning the blocked-impurity band concept, 3 conversely, as an example of generator there are phosphorus or gallium impurities in silicon.…”

Applications for quantum cascade lasers and detectors in mid-infrared high-resolution heterodyne astronomy

“…In contrast to the photoconductive QWIPs, which involve a bound to quasibound optical transition, the QCD is based on a bound to bound transition, whose excited state is resonantly coupled to an extraction cascade (phonon stair) transporting electrons vertically to the ground state of the next spatial period of the quantum cascade. As the QCD operates in a photovoltaic mode, no bias has to be applied, resulting in zero dark current and consequently no dark-current [10], and are now available in three different material systems (GaAs/AlGaAs, InGaAs/InAlAs and InGaAs/AlAsSb) covering a large wavelength range between 2.2 and 84 µm. First tests [11] were done with a device operating at 16.5 µm and using miniband-based vertical transport.…”