We report the growth of the half-Heusler alloy NiMnSb on InP ͑001͒ by molecular-beam epitaxy using a lattice-matched ͑In,Ga͒As buffer. High-resolution x-ray diffraction confirms a high crystalline quality. Spot-profile analysis low-energy electron diffraction measurements show well-defined surface reconstructions. The samples show the expected high Curie temperature and an uniaxial anisotropy.

We present room temperature resonant tunneling of GaSb/AlAsSb double barrier resonant tunneling diodes with pseudomorphically grown prewell emitter structures comprising the ternary compound semiconductors GaInSb and GaAsSb. At room temperature, resonant tunneling is absent for diode structures without prewell emitters. The incorporation of Ga 0.84 In 0.16 Sb and GaAs 0.05 Sb 0.95 prewell emitters leads to room temperature resonant tunneling with peak-to-valley current ratios of 1.45 and 1.36 , respectively. The room temperature operation is attributed to the enhanced Γ -L-valley energy separation and consequently depopulation of L-valley states in the conduction band of the ternary compound emitter prewell with respect to bulk GaSb. a) Electronic mail to: Andreas. Pfenning@physik.uni-wuerzburg.de b) Electronic mail to: Fabian.Hartmann@physik.uni-wuerzburg.de The three semiconductors GaSb, InAs and AlSb of the so-called 6.1 Å family cover a wide range of bandgap energies and unique material properties, which make them particularly suitable for applications in high-speed electronics and as mid-infrared optoelectronic semiconductor devices. 1,2 During the past few years, application related research focused on mid-infrared light sources and detectors. 3,4 Especially the progress on interband cascade lasers (ICLs) and interband cascade detectors (ICDs) with type-II superlattice absorbers has driven the field. [5][6][7] In a recent publication we proposed an alternative mid-infrared photodetector concept based on resonant tunneling diodes (RTDs) with 6.1 Å family semiconductors. 8 RTDs can be exploited as highspeed and low-noise amplifiers of weak, optically excited electrical signals. 9-11 Unlike avalanche photodiodes, in which the multiplication gain originates from impact ionization, the RTD photodetection principle is based on the modulation of the resonant tunneling current via Coulomb interaction in presence of photogenerated minority charge carriers. [12][13][14] This mechanism provides very high amplification factors exceeding several hundred thousand at considerably low operation voltages. 10,11,15,16 The GaSb/InAs/AlSb material system has brought forth resonant tunneling structures (RTS) with unique and enhanced characteristics. prewell emitters leads to room temperature resonant tunneling with peak-to-valley current ratios of 1.45 and The HR-XRD spectrum of RTD 1 shows a single peak at Δ 0°, which indicates a good and high quality latticematched crystal growth of the RTD and the AlGaAsSb contact region. For RTD 2 and RTD 3, compressive and tensile strain secondary patterns arise at smaller and higher angles, respectively, caused by the incorporation of the pseudomorphically GaInSb and GaAsSb regions. The secondary pattern of RTD 2 is more pronounced compared to RTD 3 due to the three times higher In compared to As concentration.Circular RTD mesa structures with diameters from 2 µm up to 13 µm are defined by optical lithography and dry-chemical etching. The etching depth is about 50 nm below the dou...

The structural and magnetic properties of NiMnSb films, 5-120 nm thick, grown on InGaAs/ InP͑001͒ substrates by molecular-beam epitaxy, were studied by x-ray diffraction, transmission electron microscopy ͑TEM͒, and ferromagnetic resonance ͑FMR͒ techniques. X-ray diffraction and TEM studies show that the NiMnSb films had the expected half-Heusler structure, and films up to 120 nm were pseudomorphically strained at the interface, greater than the critical thickness for this system, about 70 nm ͑0.6% mismatch to InP͒. No interfacial misfit dislocations were detected up to 85 nm, however, relaxation in the surface regions of films thicker than 40 nm was evident in x-ray reciprocal space maps. TEM investigations show that bulk, planar defects are present beginning in the thinnest film ͑10 nm͒. Their density remains constant but they gradually increase in size with increasing film thickness. By 40 nm these defects have overlapped to form a quasicontinuous network aligned closely with ͗100͘ in-plane directions. The associated strain fields and or compositional ordering from these defects introduced a reduction in crystal symmetry that influenced the magnetic properties. The in-plane and perpendicular FMR anisotropies are not well described by bulk and interface contributions. In thick films, the in-plane uniaxial and fourfold anisotropies increased with increasing film thickness. The lattice defects resulted in a large extrinsic magnetic damping caused by two-magnon scattering, an increase in the coersive field with increasing film thickness, and a lower magnetic moment ͑3.6 Bohr magnetons͒ compared to the expected value for the bulk crystals ͑4 Bohr magnetons͒.

Thin pseudomorphic ZnSe films can be grown by molecular beam epitaxy on GaAs(001) up to a layer thickness of about 100 nm. Above this critical thickness the topmost layers relax by forming large mosaic-domains which are tilted by % 0.2 with respect to the macroscopic surface. This is evidenced by satellites arising in discrete directions close to the fundamental diffraction spots in high resolution low energy electron diffraction (SPA-LEED). Energy dependent SPA-LEED measurements were performed to characterize the satellites and identify their origin. High resolution X-ray diffraction (HRXRD) experiments indicate that this mosaicity is restricted to a near-surface region and does not penetrate deeply into the bulk of the ZnSe film.

We investigate the electronic transport properties of GaSb/AlAsSb double barrier resonant tunneling diodes with pseudomorphically grown ternary GaAsxSb1 x emitter prewells over a broad temperature range. At room temperature, resonant tunneling is observed and the peak to valley current ratio (PVCR) is enhanced with increasing As mole fraction from (GaAs0. GaSb/AlSb double barrier resonant tunneling structure with a narrow bandgap absorption region. 5 The RTD photodetection principle provides high internal carrier amplification at considerably low operation voltages, [6][7][8][9] and is based on a large resonant tunneling current, that is modulated by photogenerated minority charge carriers. 10,11 Besides the amplification of optically generated charge carriers, alternative sensor schemes and operation modes can be utilized in RTD photodetectors that exploit the region of negative differential conductance (NDC). The NDC region provides the means to use stochastic resonance principles and to operate RTDs as optoelectronic switches. 12-14 Unfortunately most RTDs and resonant interband tunneling diodes (RITDs) of the 6.1 Å family are poorly suited as photodetectors because of their staggered or even broken bandgap alignment. Although these tunneling diodes show remarkable electronic properties with peak to valley current ratios above 20 at room temperature and an aptitude for RTD high frequency applications, the bandgap