Quantum Hall Dual-Band Infrared Photodetector Chiu-Chun Tang, 1 K. Ikushima, 2 D. C. Ling, 3 C. C. Chi, 1 and Jeng-Chung Chen 1 1 Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan 2 Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan 3 Department of Physics, Tamkang University, Tamsui District, New Taipei City 25137, Taiwan (Received 25 May 2017; revised manuscript received 11 September 2017; published 1 December 2017) We have developed a hybrid quantum Hall midinfrared (QHMIR)–quantum Hall far-infrared (QHFIR) photodetector by the use of graphene-GaAs=ðAl; GaÞAs–layered composite material. Both MIR and FIR photoresistance are observed in a single chip by utilizing cyclotron resonance in the quantum Hall regimes of graphene and two-dimensional electron gas (2DEG) in GaAs=ðAl; GaÞAs heterostructure, respectively. By cooperatively operating 2DEG as a back-gate electrode to change the carrier density of graphene or graphene as a top-gate electrode to modulate the carrier density of 2DEG with an applied gate voltage less than 1 V and applying the magnetic field to tune cyclotron resonance, we achieve a wide frequency selectivity, covering 640–790 cm -1 for the graphene-QHMIR detector and 24–89 cm -1 for the 2DEG- QHFIR detector. Moreover, our design integrates a log-periodic antenna with the detector to minimize the device size, while preserving high sensitivity. Our results pave the way for implementing a highly tunable MIR-to-FIR photodetector and a dual-band (MIR-FIR) imaging array. DOI: 10.1103/PhysRevApplied.8.064001 I. INTRODUCTION Indefatigable research efforts in infrared (IR) technolo- gies to develop and exploit advanced IR detectors for fundamental research and applications have persisted for decades [1]. An ultimate IR detector should possess high responsivity R v , low noise-equivalent power (NEP), high and tunable specific detectivity D à , and preferably higher operating temperatures. Nevertheless, the trade-off among these figures of merit in various types of IR detectors— mostly due to material limitations—always has to be considered in practical use. Quantum Hall infrared (QHIR) detectors based on cyclotron resonance (CR) of two-dimensional electron gas (2DEG) are known to be very sensitive and frequency selectable [2,3]. For example, typical QHIR detectors made of GaAs-based 2DEG have been reported for operation at the far-infrared (FIR) band of 27 - 102 cm -1 , tuned by external magnetic field B [4]. The optimal performance of the QHFIR photodetector has been achieved with a high R v of ∼10 8 V=W and a NEP of ≤ 10 -14 W=Hz 1=2 at 4.2 K [2]. Recent advances in the search of cooling technologies and novel low-dimensional materials significantly foster the implementation of QHFIR detectors and enrich their detection spectrum. First, nowadays, refrigeration has become more accessible due to the invention of cryogen-free systems [5]. Second, distinct quantum Hall states (QHSs) in various low-dimensional materials with different CR frequencies, such as graphene [6], atomically thin black phosphorus [7], topological insulators [8], and 2DEG at oxide interfaces [9] have been recently discovered and shed new light on developing innovative photodetec- tors. Therefore, it is conceptually feasible to implement a hybrid QHIR detector by stacking conventional semicon- ductor heterostructures and one of the new 2D materials to achieve a wide spectra range of photodetection. To date, however, the attention of such research has not been geared towards this aspect [10]. In this work, we implement a hybrid quantum Hall detector by stacking graphene on GaAs=ðAl; GaÞAs heterostructure embedded with 2DEG, as illustrated in Fig. 1(a), where a 2DEG layer and graphene are capaci- tively coupled. Graphene has attracted a great deal of attention for constructing innovated optoelectronics due to its high carrier mobility [11], broad absorption spectrum [12], and high thermal sensitivity [10]. In addition, graphene and GaAs-2DEG hold distinctly different Landau-level (LL) energies: E gr N ¼ sgnðNÞv F ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2eℏBjNj p for graphene and E 2D n ¼ðn þ 1=2Þℏω 2D c for 2DEG, where v F is the Fermi velocity of graphene, ℏ is Planck’ s constant, N and n are Landau-level indices of graphene and 2DEG, respectively, ω 2D c ¼ eB=m à is the cyclotron frequency of 2DEG with the effective mass m à (∼0.067m 0 , where m 0 is the free-electron mass), and B is the magnetic field perpendicular to the sample surface. Figure 1(b) shows E 2D n and E gr N as a function of B. It can be readily seen that at B ¼ 8 T, the first LL energy spacing for graphene is ΔE gr ¼ ℏω gr c ¼ v F ffiffiffiffiffiffiffiffiffiffiffi 2eℏB p ð ffiffiffiffiffiffiffiffiffiffiffi N þ 1 p - ffiffiffiffi N p Þ ∼ 100 meV (for N ¼ 0 → 1), and ΔE 2D ∼ 25 meV, which corresponds to the photon frequency f in the midinfrared (MIR) and far- infrared (FIR) range, respectively. Because of a large discrepancy in CR frequency between 2DEG and graphene, the photoresponse of the two materials is expected to be observed at different IR bands. Consequently, the combi- nation of graphene and 2DEG provides a platform to realize PHYSICAL REVIEW APPLIED 8, 064001 (2017) 2331-7019=17=8(6)=064001(8) 064001-1 © 2017 American Physical Society