Achieving Ultrahigh Carrier Mobility in Two-Dimensional Hole Gas of Black Phosphorus

Abstract

Abstract:We demonstrate that a field effect transistor ( Main Text:Few-layer black phosphorus (BP) has received in recent years much attention due to its unique properties making this layered material attractive for technological applications(1-3). This twodimensional crystal has an anisotropic structure (Fig.1a) and is characterized by a BP thickness dependent direct band gap(4). In contrast to graphene, the presence of a band gap in BP permits for a selective depletion of charge carriers by electrostatic gating, which is an essential feature in field effect transistors (FETs). A high charge carrier mobility reaching 1000 cm 2 /Vs at room temperature accentuates this material for applications at room temperature(5). However, the exposure of BP crystals to ambient conditions causes the oxidation of BP and significantly degrades the quality of BP channels. Nevertheless, the encapsulation of BP layers by hexagonal boron nitride (h-BN) sheets in air or in an inert gas environment is found to be very effective for preventing BP oxidation(6-8). Surface impurity effects are largely reduced, and high charge carrier mobility up to several 10 3 cm 2 /Vs has been obtained in BP FETs at cryogenic temperature(6-8). The charge carrier scattering at the impurities encapsulated along with the BP layers hinders further mobility increase. Figure 1a shows Fig.1c). The mobility values are more than four times larger compared with that in previous studies, which indicates the improved quality of h-BN/BP interfaces(7). In spite of using the advanced fabrication technique,  FET and  H saturate at T<20 K, which implies that the disorder scattering dominates over the phonon scattering in this temperature regime, which limits the hole mobility at cryogenic temperature(9). The increase of  H with the carrier density p (Fig. 1c) suggests that the disorder potential is likely created by residual impurities and can be screened by the mobile carriers (7,10,11). The scattering behavior changes at high temperatures (T>100 K).  FET and  H decrease with increasing T and follow the dependence T    , where  =1.9 and 2.0 characterize the dependence for  H and  FET , respectively (black line in Fig. 1c). The large  values imply that the acoustic phonon rather than the optical phonon scattering dominates over the scattering by the residual impurities in this temperature regime. It is very noticeable that the room temperature hole mobility  H = 5200 cm 2 /Vs closely approaches the theoretically predicted hole mobility for a clean five-layer BP sheets, which lies in the range between 4,800 cm 2 V -1 s -1 and 6,400 cm 2 V -1 s -1 (9). The realization 4 of the predicated mobility value, which is solely limited by the phonon scattering at room temperature, is another demonstration of the improved BP heterostructure quality. Quantum Hall Effect (QHE) in BP 2DHGFigure 2a shows Hall resistance R yx and magnetoresistance R xx as a function of the magnetic field, which is measured in a clean heterostructure at the base temperature of the experim...

Optical and Optoelectronic Properties of Black Phosphorus and Recent Photonic and Optoelectronic Applications

“…For the former, organic molecules or metal ions are usually employed to passivate the BP surface and meanwhile modify the optical/electrical properties of BP; for the latter, the atomic layer deposition of dielectric layer such as Al 2 O 3 , the spin coating of polymer, or the vdW capping with hBN layer has been developed to provide effective protection . In fact, the best mobility to date of few‐layer BP is observed from the h BN–BP– h BN heterostructure . Benefiting from the reduced scattering centers and charge traps at the interfaces with h BN and effective protection from the outside environment, this sandwiched structure can significantly improve the performance of electrical and optical devices.…”

Black Phosphorus Radio Frequency Electronics at Cryogenic Temperatures

“…An extrinsic peak f T of 8 GHz before de-embedding is obtained from the frequency at which |h 21 | rolls off to unity, which is over two times larger than the topgate devices shown in Figure 1c,d. [6,21,22,29] However, the radiofrequency response of BP RF transistors has been limited at room temperature to date and remained unexplored at low temperatures. [6,21,22,29] However, the radiofrequency response of BP RF transistors has been limited at room temperature to date and remained unexplored at low temperatures.…”

“…[19] As shown in previous studies, electric performance of BP FETs can be dominated by the channel dielectric interface where ALD high-κ dielectrics performs better than conventional SiO 2 . [6,21,22] However, this approach requires multiple dry transfer steps for both black phosphorus and hexagonal boron nitride flakes with precise alignment for a single device, and thus it has extremely low throughput and yield.In this paper, we report a new approach toward high-performance BP RF transistors using a Damascene-like planarization process to create an embedded gate stack with high-κ dielectrics, which enables high-quality interface while avoids the precursor exposure to the BP channel surface at the same time. [11,20] Also, encapsulation by hexagonal boron nitride results in great enhancement of the hole mobility of BP.…”

CaP3: A New Two-Dimensional Functional Material with Desirable Band Gap and Ultrahigh Carrier Mobility

“…[1][2][3][4][5][6][7][8][9][10] For example, monolayer phosphorene has been shown to possess novel electronic properties, 1,[11][12][13][14][15][16][17][18][19] including a desired bandgap of 1.51 eV, as well as high carrier (hole) mobilities in the range of 10000-26000 cm 2 V -1 s -1 . 14 Indeed, few-layer black phosphorus field-effect transistors have been successfully fabricated, 13,[18][19][20] which give rise to drain current modulation up to 10 5 and hole mobility up to 5200 cm 2 V -1 s -1 . 13,20 Today, the quest for new 2D atomic-layer materials that possess both desired direct bandgap and high carrier mobilities is still a highly active area of research.…”