Experimental studies on aluminum (Al) and boron (B) implantation in 4H/6H SiC are reported; the implantation is conducted at room temperature or elevated temperatures (500 to 700 °C). Both Al and B act as “shallow” acceptors in SiC. The ionization energy of these acceptors, the hole mobility and the compensation in the implanted layers are obtained from Hall effect investigations. The degree of electrical activity of implanted Al/B atoms is determined as a function of the annealing temperature. Energetically deep centers introduced by the Al+/B+ implantation are investigated. The redistribution of implanted Al/B atoms subsequent to anneals and extended lattice defects are monitored. The generation of the B‐related D‐center is studied by coimplantation of Si/B and C/B, respectively.

A continuously operated tubular crystallizer system with an inner diameter of 2.0 mm has been successfully operated. It allows the crystallization of active pharmaceutical ingredients (APIs) under controlled conditions. Acetylsalicylic acid (ASA) which was crystallized from ethanol (EtOH) was used as the model substance. An ethanolic suspension of ASA-seeds was fed into the tubular crystallizer system, where it was mixed with a slightly undersaturated ASA-EtOH solution that was kept at an elevated temperature in its storage vessel. Supersaturation was created via cooling and the seeds grew to form the product crystals. This work mainly focuses on the proof-of-concept and on the impact of the flow rates on the product crystals and the crystal size distribution (CSD). All other parameters including concentrations, temperatures, and loading of seeds were kept constant. Higher flow velocities generally resulted in reduced number and volume mean diameters, due to reduced tendency of agglomeration and decreased time for crystal growth due to shorter residence times of the suspension in the tube. Generally, all experiments unmistakably led to shifting of volume density distributions toward significantly larger values for product crystals in comparison to the seeds and were capable of yielding product masses in a g/min scale.

Comparative Hall effect investigations are conducted on N- and P-implanted as well as on (N+P)-coimplanted 4H–SiC epilayers. Box profiles with three different mean concentrations ranging from 2.5×1018 to 3×1020 cm−3 to a depth of 0.8 μm are implanted at 500 °C into the (0001)-face of the initially p-type (Al-doped) epilayers. Postimplantation anneals at 1700 °C for 30 min are conducted to electrically activate the implanted N+ and P+ ions. Our systematic Hall effect investigations demonstrate that there is a critical donor concentration of (2–5)×1019 cm−3. Below this value, N- and P-donors result in comparable sheet resistances. The critical concentration represents an upper limit for electrically active N donors, while P donors can be activated at concentrations above 1020 cm−3. This high concentration of electrically active P donors is responsible for the observed low sheet resistance of 35 Ω/□, which is about one order of magnitude lower than the minimum sheet resistance achieved by N implantation.

The bonding of nitrogen in low N-content AlxGa1−xAs1−yNy with x⩽0.05 and y⩽0.04 has been studied by Raman spectroscopy. Upon the addition of Al to GaAsN, additional vibrational modes are observed at around 450 cm−1, which is below the GaN-like longitudinal optical (LO) phonon mode centered at 470 cm−1. These modes are attributed to the formation of Al and N containing complexes with Al-to-N bonding. With increasing Al content the Al–N related modes gain intensity at the expense of the GaN-like mode, and they become the dominant N-related feature for an Al-content of 5% at a fixed N content of 1%. On the other hand, increasing the N content from 0% up to 4% at a constant Al concentration of 5% results first in the appearance and eventual saturation in intensity of the AlN-like modes, accompanied by a steep increase in intensity and eventual dominance of the GaN-like vibrational mode. Simultaneously the AlAs-like LO2 phonon mode shows a drastic decrease in intensity for N contents exceeding 2%. All these observations strongly indicate that there is a preferential formation of Al–N bonds in low N- and Al-content AlGaAsN, which is in direct contrast to GaInAsN, where even after thermal annealing the GaN-like mode remains dominant in the Raman spectrum compared to the InN-like modes.

Nonthermal rollover (or efficiency droop) of the electroluminescence (EL) efficiency has been investigated for near-UV-emitting (AlGaIn)N single-well light-emitting diodes (LED) with varying GaInN well widths grown on substrates with different dislocation densities (DDs). For each DD the well width of the mesa-LEDs has been optimized for maximum EL efficiency at high operating currents. LEDs on freestanding GaN (DD 4 x 10(exp 7) cm-2) with an 18 nm thick GaInN wide-well active region show the highest efficiency, and the output power-versus-current characteristic remains linear up to the highest pulsed current density of 750 A/cm2. In contrast, LEDs on sapphire grown with conventional low-temperature nucleation (DD 10(exp 9) cm-2) exhibit the optimum well width a 3 nm and show significant nonthermal rollover

Dilute InAs(1-y)N(y) and high In-content Ga(1-x)In(x)As(1-y)N(y) layers with y lt = 0.012 and x gt= 0.92 were grown by rf-nitrogen plasma source molecular-beam epitaxy on InP substrates using a metamorphic GaInAs buffer layer. The bonding of nitrogen in these alloys was analyzed by Raman spectroscopy, showing that nitrogen is incorporated in dilute InAsN as isolated N(As) for a nitrogen content of y = 0.005; two additional nitrogen-related modes were found to appear at higher nitrogen contents (y=0.012), possibly due to the formation of higher-order di-nitrogen In-N complexes. The addition of a small amount of Ga to the InAsN ([Ga] lt = 8%) was found to lead to an almost complete change from pure In-N bonding to a preferential bonding of the substitutional nitrogen to at least one Ga neighbour. Further, the effect of nitrogen incorporation on the higher-lying E(ind 1) and E(ind 1) + delta(ind 1) interband transitions of InAsN has been studied by spectroscopic ellipsometry, revealing a high-energy shift of both interband transitions with increasing nitrogen content at a rate similar to that reported for dilute GaAsN

The influence of the Mg doping profile on the electroluminescence (EL) efficiency of (AlGaIn)N quantum well (QW) light-emitting diodes, grown by low-pressure metal-organic vapor-phase epitaxy on sapphire, has been investigated. The actual Mg profile close to the active region was found to be influenced by segregation as well as by diffusion during growth. In a first experiment, diffusion of the Mg dopants towards the QW region through a not intentionally doped narrow GaN spacer layer, separating the topmost GaInN quantum well from the AlGaN:Mg electron-blocking barrier, was controlled by the growth temperature of the AlGaN:Mg barrier and GaN:Mg contact layer. Starting from low growth temperatures, an increase in Mg concentration close to the active region results in an improved hole injection and thus increased EL efficiency. However, for a too high growth temperature, an excessive spread of the Mg atoms into the active region leads to nonradiative recombination in the QW active region and thus a reduction in EL output. In a second experiment, identical structures were prepared with the Mg-doped (Al)GaN layers grown at lower temperature to minimize Mg diffusion. Instead, the nominal Mg doping level in the GaN spacer layer was varied systematically. Secondary-ion-mass spectrometry revealed that almost identical Mg doping profiles close the QW active region, and in turn very similar EL efficiencies, can be achieved by both approaches when appropriate growth parameters are used.

We prepared epitaxial ferromagnetic manganite films on 45 • bicrystal substrates by pulsed laser ablation. Their low-and high-field magnetoresistance (MR) was measured as a function of magnetic field, temperature and current. At low temperatures hysteretic changes in resistivity up to 70 % due to switching of magnetic domains at the coercitive field are observed. The strongly non-ohmic behavior of the current-voltage (I-V ) leads to a complete suppression of the MR effect at high bias currents with the identical current dependence at low and high magnetic fields. We discuss the data in view of tunneling and mesoscale magnetic transport models and propose an explicit dependence of the spin polarization on the applied current in the grain boundary region.