Weixuan Hu

GeSn p-i-n photodetector for all telecommunication bands detection

Using a 820 nm-thick high-quality Ge0.97Sn0.03 alloy film grown on Si(001) by molecular beam epitaxy, GeSn p-i-n photodectectors have been fabricated. The detectors have relatively high responsivities, such as 0.52 A/W, 0.23 A/W, and 0.12 A/W at 1310 nm, 1540 nm, and 1640 nm, respectively, under a 1 V reverse bias. With a broad detection spectrum (800-1800 nm) covering the whole telecommunication windows and compatibility with conventional complementary metal-oxide-semiconductors (CMOS) technology, the GeSn devices are attractive for applications in both optical communications and optical interconnects.

Large reversible magnetocaloric effect in Tb3Co compound

A large reversible magnetocaloric effect has been observed in Tb(3)Co compound. Under a magnetic field change of 5 T, the maximum value of magnetic entropy change Delta S(M) is -18 J kg(-1) K(-1) at 84 K and the relative cooling power is 738 J kg(-1) with no hysteresis loss. In particular, the large reversible Delta S(M)(max), -8.5 J kg(-1) K(-1), is achieved for a low magnetic field change of 2 T. The magnetic anisotropy and the texture of the material greatly affect Delta S(M). The large reversible magnetocaloric effect (both the large Delta S(M) and the high relative cooling power) indicates that Tb(3)Co could be a promising candidate for magnetic refrigeration

Large reversible magnetocaloric effect in TbCoC2 in low magnetic field

A large reversible negative magnetic-entropy change Delta S(M) has been observed in TbCoC(2), accompanied by a second-order phase transition at 28 K. The maximum value of -Delta S(M) is 15.3 J kg(-1) K(-1) at 30 K for a magnetic-field change from 0 to 5 T, with the refrigerant capacity of 354 J kg(-1). In particular, also the large -Delta S(M)(max) of 7.8 J kg(-1) K(-1), is obtained for a small field change from 0 to 2 T. The large reversible Delta S(M) and the high reversible refrigerant capacity in low magnetic field indicate that TbCoC(2) may be a promising candidate for magnetic refrigeration at low temperatures

Magnetocaloric effect in Ho2In over a wide temperature range

The compound Ho(2)In exhibits two successive magnetic phase transitions: a spin-reorientation transition at T(SR)=32 K and a magnetic-ordering transition at T(C)=85 K. The maximum reversible -Delta S(M) values are 6.3 and 11.2 J/kg K at T(SR) and T(C), respectively, for a field change of 5 T. These two -Delta S(M) peaks with the same sign are partly overlapping, which results in a wide temperature interval with appreciable magnetocaloric effect. The results on Ho(2)In indicate that materials with successive SR and magnetic-ordering transitions may constitute an important new class of magnetic refrigerants since they work in a wider temperature range than the conventional refrigerant materials.

Electroluminescence from Ge on Si substrate at room temperature

A Ge/Si heterojunction light emitting diode with a p(+)-Ge/i-Ge/N+-Si structure was fabricated using the ultrahigh vacuum chemical vapor deposition technology on N+-Si substrate. The device had a good I-V rectifying behavior. Under forward bias voltage ranging from 1.1 to 2.5 V, electroluminescence around 1565 nm was observed at room temperature. The mechanism of the light emission is discussed by the radiative lifetime and the scattering rate. The results indicate that germanium is a potential candidate for silicon-based light source material

Ferromagnetism and superparamagnetism of ZnCoO:H nanocrystals

ZnCoO:H nanocrystals are weak ferromagnetic at room temperature with a small coercivity and a small remanence, whereas ZnCoO nanocrystals are paramagnetic. The thermal irreversibility of zero-field cooling and field cooling magnetizations of ZnCoO:H nanocrystals corresponds to the existence of superparamagnetism due to the nanosize effect. X-ray photoelectron spectra show the incorporation of Co(2+) ions inside the ZnO lattice without changing the wurtzite structure. Our data suggest that hydrogen can induce ferromagnetism in ZnCoO and that ferromagnetic ZnCoO:H crystals with small particle size can show the superparamagnetism

Large low-field inverse magnetocaloric effect in Ni 50−x Mn 38+x Sb 12 alloys

The magnetic properties and magnetocaloric effects of Ni(50-x)Mn(38+x)Sb(12) ferromagnetic shape-memory alloys with x = -1, 0, 1 and 2 that undergo a martensitic transformation were investigated. The magnetic-entropy changes Delta S of nominal Ni(49)Mn(39)Sb(12), or Ni(49.5)Mn(38.6)Sb(11.9), at 279K is 6.15 J kg(-1) K(-1) for a magnetic-field change Delta B = 1 T, with negligible hysteresis loss, as it transforms from a low-temperature martensitic phase to a high-temperature austenitic one. The large inverse Delta S in a small field change and the negligible hysteresis loss, along with the low cost of Sb, indicate that Ni(49)Mn(39)Sb(12) is a promising candidate for room-temperature magnetic refrigeration.

Giant reversible magnetocaloric effect in cobalt hydroxide nanoparticles

The magnetocaloric effect associated with magnetic phase transitions in -CoOH 2 nanoparticles has been investigated. A sign change in the magnetocaloric effect is induced by a magnetic field, which is related to a field-induced transition from the antiferromagnetic to the ferromagnetic state below the Neel temperature. The large reversible magnetic-entropy changeS m 20.9 J /kg K at 15 K for a field change of 7 T indicates that -CoOH 2 is a potential candidate for application in magnetic refrigeration in the low-temperature range.

Magnetic properties and exchange bias in Mn2O3∕Mn3O4 nanoclusters

Mn(2)O(3)/Mn(3)O(4) nanoclusters were prepared by air oxidation of Mn(3)O(4) nanoparticles. The nanoparticles located at the surface of the Mn(2)O(3)/Mn(3)O(4) nanoclusters are oxidized to Mn(3)O(4) to form the special structure of the Mn(2)O(3)/Mn(3)O(4) nanoclusters. An exchange bias was observed in the Mn(2)O(3)/Mn(3)O(4) nanoclusters, which was induced by exchange coupling between ferromagnetic Mn(3)O(4) and antiferromagnetic Mn(3)O(4) phases

Room temperature direct-bandgap electroluminescence from n-type strain-compensated Ge/SiGe multiple quantum wells

N-type strain-compensated Ge/Si0.15Ge0.85 multiple quantum wells (MQWs) were grown on a Si0.1Ge0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition on a n+-Si(001) substrate. Under low forward bias voltage ranging from 0.6 to 1.2 V, narrow direct-bandgap electroluminescence (EL) peak from MQWs light emitting diode was observed at room temperature. The quantum confinement effect of the direct-bandgap transitions and the temperature dependent EL peak redshift are in good agreement with the calculated results.