P. J. van Hall

Scattering of polarized protons by iron and nickel isotopes

Abstract Elastic and inelastic scattering of polarized protons ( E = 17.2, 20.4, 24.6 MeV) by 54, 56 Fe and 58, 60, 62 Ni have been investigated. Most data can be readily accommodated by standard optical-model and DWBA procedures, including full Thomas coupling. The 2 + 1 state (1.41 MeV) in 54 Fe is peculiar because the inelastic scattering data require deformation parameters for the central and spin-orbit parts of the nuclear potential that differ by a factor 2 to 3; moreover, this anomaly shows a marked energy dependence.

Carrier‐carrier scattering induced capture in quantum well lasers

We present calculations of the carrier capture efficiency into various types of quantum well lasers. The carrier capture into a quantum well can be due to either optical phonon emission or carrier‐carrier scattering. Both capture mechanisms have been calculated and show oscillations as a function of the quantum well thickness. By optimizing the carrier capture efficiency the carrier accumulation in the barrier layers can be reduced, resulting in an improved modulation response and threshold current.

Remote impurity scattering in heterojunctions

The commonly used formalism for the ionised remote impurity scattering of electrons in a 2D electron gas contains the following inconsistency. The potential of the donors (e.g. the Si donors in the AlGaAs in the case of a GaAs-AlGaAs heterojunction) is accounted for twice: first in the self-consistent calculation of the envelope function and secondly in the calculation of the scattering rate. Instead, only the scattering as due to the fluctuations in the average field of the donors should be accounted for. The authors have developed expressions for this scattering amplitude and have applied them to a few GaAs-AlGaAs samples with very high mobilities. These samples posed the problem of a serious underestimation of the experimental mobility by the theory. This problem now can be resolved and a better agreement between experiment and theory has been obtained.

Study of the 118Sn(p, α)115In reaction with 20 MeV polarized protons

Abstract The analyzing powers in the 118 Sn(p, α ) reaction leading to five states in 115 In have been measured at E p = 20.4 MeV. The results are well described with DWBA calculations using a cluster form factor.

Investigations on indium phosphide grown by chemical beam epitaxy

In this paper, we present a systematic study of the properties of indium phosphide (InP) layers grown by chemical beam epitaxy (CBE). Trimethylindium (TMIn) and phosphine (PH3) are used as source materials. The relation between the phosphine cracker temperature and the cracking efficiency has been studied by mass spectroscopy during growth. The growth rate and morphology of the layers have been studied by varying the TMIn and phosphine flow rates as well as the substrate temperature. We have found that, under a wide range of growth conditions, the deposition rate is only determined by and proportional to the TMIn flow rate. This is in agreement with literature. Additionally, we observe that the growth rate decreases below a certain phosphine to TMIn flow rate (V/III) ratio and becomes phosphine flow limited. From investigations of the growth rate as a function of temperature, it is concluded that the desorption of indium species from InP starts at a temperature slightly below 540°C. For this desorption process, we have found an activation energy of (217 ± 20) kJ/mol. Further characterization of the InP layers has been carried out by photoluminescence and Hall measurements. From both methods, the optimum growth conditions have been established. Under these conditions, we reproduc-ibly obtain InP layers showing linewidths of the donor-bound exciton transition at 5K around 0.25 meV and a mobility at 77K of about 7.0·104 cm2/Vs. From the analysis of the mobility in the temperature range from 20 to 300K, we conclude that, additionally to shallow donors and acceptors, deep-donor centers with an activation energy of about 150 meV are present in all layers.

Scattering of 22.3 MeV polarized protons from the even-mass cadmium isotopes 106-116Cd

Measurements have been done on polarized-proton scattering from the even-mass cadmium isotopes 106-116Cd, at a beam energy of 22.3 MeV. The experimental data were analysed using first- and second-order vibrational models in a coupled-channels formalism. The 01+, 21+ and 31- levels are represented satisfactorily by theory. In 106-116Cd the 22+ and 41+ levels were resolved; for the 22+ levels the theory systematically underestimates the first diffraction maximum of the cross section at 30 degrees while the 41+ levels are reproduced reasonably well. In 112-114Cd the 02+ level could also be studied; there are indications for a strong coupling between the two-phonon 0+ state in the ground-state band and the 0+ head of the intruder band. In 114Cd we also investigated the 23+ level, probably the first excited state of the intruder system, which showed an angular pattern with more pronounced details than the 21+ states. Finally in 112Cd the 11

Remote impurity scattering in GaAsAlGaAs heterojunctions

and 51- levels were studied which have a strong direct coupling to the ground state.

Scattering of 21.1 MeV polarized protons from 89Y

Abstract In this paper we present a revised formulation of the remote impurity scattering in GaAsAlGaAs heterojunctions. The formalism is applied to various experimental results with considerable success.

Ultrafast carrier dynamics at a metal-semiconductor interface studied by femtosecond luminescence spectroscopy

Abstract The elastic and inelastic scattering of 21.1 MeV protons from 89Y have been investigated. The excited states with a collective nature can be described quite well with standard OM and DWBA techniques. The transitions to the low-lying single-particle states are described with antisymmetrized microscopic DWBA including tensor and spin-orbit forces. The agreement with the experimental data is encouraging.

ULTRAFAST CARRIER DYNAMICS AT A METAL-SEMICONDUCTOR INTERFACE

The ultrafast carrier dynamics in the high electric field at an Au-GaAs interface has been studied both experimentally, using a subpicosecond photoluminescence correlation technique, and theoretically by a Monte Carlo simulation. The photoluminescence decay time has been found to increase drastically with input power, ranging from a few picoseconds at low excitation to a considerably higher value (10-20 ps) at high excitation. From the Monte Carlo calculations it has been found that at high excitation the applied field collapses almost instantaneously. Even for a recharging time constant of 1 ps, which corresponds to the estimated device RC time, a drastic slowing down of the carrier sweep-out has been found, in almost quantitative agreement with the experimental findings.