Without any assumptions regarding residual impurity species in an undoped semiconductor, it is experimentally demonstrated that the densities and energy levels of impurities can be precisely determined by the graphical peak analysis method based on Hall-effect measurements, referred to as free carrier concentration spectroscopy (FCCS). Using p-type undoped GaSb epilayers grown by molecular beam epitaxy (MBE), the densities and energy levels of several acceptor species are accurately determined. Five acceptor species are detected in the undoped GaSb epilayers grown by MBE, while two are also found in ptype undoped GaSb wafers. A 21-41 meV acceptor and a 75-99 meV acceptor exist both in the epilayers and in the wafer. On the other hand, a 164-181 meV acceptor is detected in epilayers grown at an Sb 4 /Ga flux beam equivalent pressure ratio of 8 or 10, while a 259 meV acceptor is found in the epilayer grown at Sb 4 /Ga = 6. In addition, a very shallow acceptor, which is completely ionized at 80 K, is found in the epilayers. The densities of the very shallow acceptor and the 21-41 meV acceptor are minimum at Sb 4 /Ga ¼ 8, which makes the hole concentration lowest in the temperature range of the measurement.

SummaryA simple, mild and versatile new tritium ( 3 H) labelling method on a micro scale using sodium borotritide (NaB 3 H 4 ) and a transition-metal complex catalyst is described. 3 H-labelled compounds were prepared effectively by 3 H hydrogenolysis of appendant functional groups in target compounds.The appendant functional group such as bromo, iodo or sulfonate in various target compounds can be replaced by tritium ( 3 H) in moderate yields. The new method was established by optimization of the reaction conditions and examination of its applicability using four types of model substrates in tracer runs. Then, various drug candidates and ligands for drug discovery were labelled with tritium on a micro scale. The specific radioactivity of the 3 H-labelled compounds used for the studies on receptor binding ranged from 12 to 20 Ci/mmol.

Without any assumptions regarding residual impurity species and intrinsic defects in an undoped semiconductor, it is experimentally demonstrated that the densities and energy levels of impurities and defects can be precisely determined by a graphical peak analysis method based on Hall-effect measurements, referred to as free-carrier-concentration spectroscopy (FCCS). By FCCS, the number of acceptor species in p-type undoped In 0:2 Ga 0:8 Sb epilayers is determined, and the densities and energy levels of these acceptor species are accurately estimated. Two acceptor species, whose acceptor levels are E V þ 25 meV and E V þ 86 meV, are detected, where E V is the valence band maximum. The density of the E V þ 25 meV acceptor increases with Sb 4 =ðIn þ GaÞ flux beam equivalent pressure (BEP) ratio, whereas the density of the E V þ 86 meV acceptor decreases with increasing BEP ratio. These observations are not consistent with the conventional assumption that these acceptor species are V Sb þ and V Sb 2þ in GaSb-based semiconductors, where V Sb is the Sb vacancy.