HfS2 is the novel transition metal dichalcogenide, which has not been experimentally investigated as the material for electron devices. As per the theoretical calculations, HfS2 has the potential for well-balanced mobility (1,800 cm2/V·s) and bandgap (1.2 eV) and hence it can be a good candidate for realizing low-power devices. In this paper, the fundamental properties of few-layer HfS2 flakes were experimentally evaluated. Micromechanical exfoliation using scotch tape extracted atomically thin HfS2 flakes with varying colour contrasts associated with the number of layers and resonant Raman peaks. We demonstrated the I-V characteristics of the back-gated few-layer (3.8 nm) HfS2 transistor with the robust current saturation. The on/off ratio was more than 104 and the maximum drain current of 0.2 μA/μm was observed. Moreover, using the electric double-layer gate structure with LiClO4:PEO electrolyte, the drain current of the HfS2 transistor significantly increased to 0.75 mA/μm and the mobility was estimated to be 45 cm2/V·s at least. This improved current seemed to indicate superior intrinsic properties of HfS2. These results provides the basic information for the experimental researches of electron devices based on HfS2.

In III-V-based magnetic semiconductors, the anomalous Hall effect (AHE) [1][2][3][4][5] has been playing a pivotal role in characterizing the magnetic properties, as was the case in our recently published Letter [6]. Since it was not made sufficiently clear that the Hall resistance loops presented were not raw data, we describe how the Hall resistance loops were obtained in our AHE measurements. In our magnetic semiconductor heterostructures, the longitudinal magnetoresistance (MR) effect is large. When we measure the Hall voltage of our samples in patterned Hall bars or in van der Pauw geometry, a large MR contribution is always superimposed on the Hall voltage data. This MR contribution results from the nonideal measurement geometry of the samples [1][2][3][4]. Thus, the raw Hall resistance R raw data (the raw Hall voltage divided by the current) in our case can be expressed as R raw B R H B R MR B. Here, R H is the intrinsic Hall resistance and R MR is the magnetoresistance (MR) contribution, which gives a nonzero value at B 0 (offset) to the raw Hall resistance R raw , and its magnetic-field dependence is an even function. Since the Hall resistivity in magnetic materials under a magnetic field applied perpendicular to the sample plane consists of the ordinary Hall effect and AHE [7], the sheet Hall resistance R H of our heterostructures can be expressed as [6,8,9]. Here, R O is the ordinary Hall coefficient, R S is the anomalous Hall coefficient, and M is the perpendicular component of magnetization of the sample. In the AHE, R H B is an odd function with respect to the polarity of the B (and also M), and thus, it is antisymmetric (or ''odd symmetric'') when a full field sweep is performed, i.e., R H B ÿR H ÿB [9]. On the other hand, R MR B is an even function with respect to the polarity of B (and also M) [1,2], and thus, it is even symmetric, i.e., R MR B R MR ÿB. Therefore, one can decompose the raw Hall resistance data R raw into the Hall resistance R H B R raw B ÿ R raw ÿB=2 and the magnetoresistance R MR B R raw B R raw ÿB=2. 2(j) show the raw Hall data R raw taken from Hall bars [as shown in Fig. 1(a), the channel width and length are 50 m and 200 m, respectively] of sample A and sample B, respectively, of Ref.[6] under a full field sweep of ÿ0:5 T B 0:5 T, which are the superposition of the intrinsic Hall resistance (R H ) and the MR contribution (R MR ). Note that the R raw curves in the figures are qualitatively similar to those observed in other 2(k) show the decomposed R H data of sample A and sample B, respectively. Figures 2(c), 2(f), 2(i), and 2(l) show the decomposed R MR data of sample B. In our Letter [6], we focused on the Hall resistance R H . In this way, we eliminated the MR contribution from the raw Hall resistance data using the method mentioned above, and plotted the intrinsic Hall resistance. Given the fact that the magnetotransport data show clear ferromagnetic hysteretic behavior and its temperature dependence together with the supporting data [10], we believe that there is ferroma...

We show that suitably designed magnetic semiconductor heterostructures consisting of Mn delta (delta)-doped GaAs and p-type AlGaAs layers, in which the locally high concentration of magnetic moments of Mn atoms are controllably overlapped with the two-dimensional hole gas wave function, realized remarkably high ferromagnetic transition temperatures (T(C)). A significant reduction of compensative Mn interstitials by varying the growth sequence of the structures followed by low-temperature annealing led to high T(C) up to 250 K. The heterostructure with high T(C) exhibited peculiar anomalous Hall effect behavior, whose sign depends on temperature.

We fabricated TM mode InGaAlAs∕InP active waveguide optical isolators based on the magnetically induced nonreciprocal loss. We used epitaxially grown MnAs thin films as ferromagnetic electrodes of the semiconductor active waveguide optical isolators. We demonstrated TM mode nonreciprocal propagation (8.8dB∕mm) at 1540nm with an excellent ferromagnetic electrode contact, which has greater semiconductor active waveguide optical isolator performance than that of our previously reported devices with Ni∕Fe polycrystalline electrodes.

A 1.5-m nonreciprocal-loss waveguide optical isolator having improved transverse-magnetic-mode (TM-mode) isolation ratio was developed. The device consisted of an InGaAlAs/InP semiconductor optical amplifier waveguide covered with a ferromagnetic epitaxial MnSb layer. Because of the high Curie temperature (T c ¼ 314 C) and strong magneto-optical effect of MnSb, the nonreciprocal propagation of 11-12 dB/mm has been obtained at least up to 70 C. # W aveguide optical isolators that can be monolithically integrated with other waveguide devices such as lasers and amplifiers are indispensable for stable operation of photonic integrated circuits (PICs). [1][2][3][4][5][6] One promising way of producing waveguide isolators is by making use of nonreciprocal propagation loss -a magneto-optical phenomenon where, in an optical waveguide combined with a ferromagnetic layer, the propagation loss of light is larger in backward than in forward propagation. On the basis of theoretical proposals, 7,8) several experiments have been reported on transverse-electric-mode (TE-mode) and transverse-magnetic-mode (TM-mode) nonreciprocal-loss isolators at 1.3-m and 1.55-m telecommunication wavelength bands. [9][10][11][12][13][14] The authors' group first built a TE-mode isolator, consisting of an InGaAsP/InP semiconductor optical-amplifying (SOA) waveguide combined with a ferromagnetic Fe layer, 9) and obtained an isolation ratio of 14.7 dB/m. 12) Encouraged by this result, we then started developing a TM-mode waveguide isolator. The key to developing the TM isolator is the selection of an appropriate ferromagnetic material because, in a device that operates in TM mode, the ferromagnetic layer is also used as a contact layer for the current injection into the SOA waveguide. Therefore, the ferromagnetic layer has to (i) have a strong magneto-optical effect along with a large saturation magnetization and (ii) provide a low-barrier contact for III-V semiconductors. Ordinary ferromagnetic metals such as Fe and Co are not suited for this purpose because they produce a Schottky barrier on III-V semiconductors resulting in a high contact resistance. In addition, they produce undesirable paramagnetic materials such as FeAs and CoAs at the contact interface and, therefore, degrade the microscopic flatness of the interface.We previously proposed using manganese-arsenide (MnAs) as the material for the ferromagnetic layer. 13,14) MnAs is a ferromagnetic intermetallic compound with a nickel-arsenide structure that can be grown epitaxially on GaAs, InP, and related semiconductors. 15) We fabricated a TM-mode device with a MnAs layer and obtained the isolation ratio of 7.2 dB/mm at a wavelength of 1.54 m. This device was, however, unable to operate at temperatures higher than room temperature (RT) because the Currie temperature of MnAs is only 40 C. Moreover, the isolation ratio obtained was not large enough for certain applications.To overcome these problems, in this paper, we have for the first time adopted manganese antimonide MnSb -a ferromagnetic c...

We fabricated GaInAsP/InP waveguide-integrated lateral-current-injection (LCI) membrane distributed feedback (DFB) lasers on a Si substrate by using benzocyclobutene (BCB) adhesive bonding for on-chip optical interconnection. The integration ofa butt-jointed built-in (BJB) GaInAsP passive waveguide was performed by organometallic vapor-phase epitaxy (OMVPE).By introducing a strongly index-coupled DFB structure with a 50-µm-long cavity, a threshold current of 230 µA was achieved for a stripe width of 0.8 µm under room-temperature continuous-wave (RT-CW) conditions. The maximum output power of 32 µW was obtained. The lasing wavelength and submode suppression ratio (SMSR) were 1534 nm and 28 dB, respectively, at a bias current of 1.2 mA.

We developed a 1.5-microm band TM-mode waveguide optical isolator that makes use of the nonreciprocal-loss phenomenon. The device was designed to operate in a single mode and consists of an InGaAlAs/InP ridge-waveguide optical amplifier covered with a ferromagnetic MnAs layer. The combination of the optical waveguide and the magnetized ferromagnetic metal layer produces a magneto-optic effect called the nonreciprocal-loss phenomenon--a phenomenon in which the propagation loss of light is larger in backward propagation than it is in forward propagation. We propose the guiding design principle for the structure of the device and determine the optimized structure with the aid of electromagnetic simulation using the finite-difference method. On the basis of the results, we fabricated a prototype device and evaluated its operation. The device showed an isolation ratio of 7.2 dB/mm at a wavelength from 1.53 to 1.55 microm. Our waveguide isolator can be monolithically integrated with other waveguide-based optical devices on an InP substrate.

We successfully demonstrated room-temperature continuous-wave (RT-CW) operation of a lateral-current-injection (LCI) GaInAsP/InP membrane Fabry–Perot laser by benzocyclobutene (BCB) adhesive bonding on a Si substrate for the first time. Our results include, for example, a threshold current of 2.5 mA and an external differential quantum efficiency of 22% per facet were obtained for a stripe width of 0.7 µm and a cavity length of 350 µm. From measurements of the differential quantum efficiency as a function of the cavity length, an internal quantum efficiency of 75% and a waveguide loss of 42 cm−1 were obtained.