Bone loss due to accidents or tissue diseases requires replacement of the structure by either autografts, allografts, or artificial materials. Reactive cements, which are based on calcium phosphate chemistry, are commonly used in nonload bearing areas such as the craniofacial region. Some of these materials are resorbed by the host under physiological conditions and replaced by bone. The aim of this study was to test different calcium and magnesium cement composites in vitro for their use as bone substitution material. Phase composition of calcium deficient hydroxyapatite (Ca(9) (PO(4) )(5) HPO(4) OH), brushite (CaHPO(4) ·2H(2) O), and struvite (MgNH(4) PO(4) ·6H(2) O) specimens has been determined by means of X-ray diffraction, and compressive strength was measured. Cell growth and activity of osteoblastic cells (MG 63) on the different surfaces was determined, and the expression of bone marker proteins was analyzed by western blotting. Cell activity normalized to cell number revealed higher activity of the osteoblasts on brushite and struvite when compared to hydroxyapatite and also the expression of osteoblastic marker proteins was highest on brushite scaffolds. While brushite sets under acidic conditions, formation of struvite occurs under physiological pH, similar to hydroxyapatite cements, providing the possibility of additional modifications with proteins or other active components.

We present resonant tunneling diode-photodetectors (RTD-PDs) with GaAs0.15Sb0.85/AlAs0.1Sb0.9 double barrier structures combined with an additional quaternary Ga0.64In0.36As0.

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...

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

We study the optical tunability of the charge carrier type in InAs/GaSb double quantum wells with its type-II broken band alignment and inverted band structure. Under constant optical excitation, the majority charge carrier type switches from electron to hole. Within the majority charge carrier type transition, the coexisting minority charge carrier contribution indicates electron-hole hybridization with a nontrivial topological insulating phase. The optical tuning is attributed to the negative photoconductivity of antimonide materials in combination with a persistent charge carrier buildup of photogenerated charges at the surface and substrate side of the device, respectively. Our study of the tuning of an InAs/GaSb double quantum well heterostructure reveals that an electro-optical switching is possible and paves the way to an optical control of the phase diagram of InAs/GaSb topological insulators.