U. Reislöhner

Band-gap level of the cadmium vacancy in CdTe

The reaction Ag Cd → Ag i + V Cd was used to create cadmium vacancies V Cd in the space charge region of a Schottky contact on p-type CdTe. At T = 380 K, the Ag i + ions were drifted out of the space charge region by the high electric field under reverse bias condition. After cooling down to 80 K with applied reverse bias, admittance spectroscopy measurements were performed. Only after this reverse bias annealing, an additional defect with a thermal activation energy of E V + 0.23(3) eV is observed. In other samples, the existence of V Cd after silver diffusion was monitored by perturbed angular correlation spectroscopy (PAC). Here, admittance spectroscopy reveals the same activation energy of the electrically dominating defects as given above. This result supports the assignment of this level to cadmium vacancy acceptors.

Complex formation at indium donors in p-CdTe

After diffusion of silver into p-CdTe at room temperature, two electric field gradients (EFG) are observed at 111 In/ 111 Cd probe atoms at T = 77 K: v Q1 = 61 MHz, η 1 = 0.15 and v Q2 = 30 MHz, η 2 = 0.46. The assignment of EFG 1 to In-A centers leads to the conclusion that the 0/ - level of the Cd-vacancy is located deeper in the band gap than the shallow doping and that the two EFGs are caused by the neutral and singly negative Cd-vacancy. The reason for In-A center formation and subsequent dissociation (aging) after Ag diffusion is explained.

Hydrogen passivation of cd acceptors in III–V semiconductors studied by PAC spectroscopy

Abstract Formation, structure, and stability of hydrogen correlated complexes, created at Cd acceptors in GaP, InP, and InAs have been studied after plasma charging as well as after H+ and/or He+ implantation at different energies. The different complexes were monitored by the perturbed angular correlation technique (PAC). In InP and Gap, the stability of Cd-H pairs is very similar for comparable Cd concentrations (ED = 1.4(2) eV and ED = 1.5(1) eV). In InAs, two different hydrogen correlated configurations are observed, one could be identified as Cd-H pair, oriented in 〈111〉 lattice direction (νQ = 427 MHz, η = 0). The second complex involves at least one H atom and radiation defects or, favoured by a defect induced, secondary mechanism several hydrogen atoms.

Damage production in GaAs during MeV ion implantation

Abstract The influence of the nuclear and electronic energy loss on the damage production in GaAs has been studied by Se + ion implantation at T I = 293 K with energies ranging from 2 MeV up to 20 MeV. The ion dose was varied between 5 × 10 12 /cm 2 and 1 × 10 15 /cm 2 . The damage production was investigated using RBS in channeling regime. Temperature and energy dependent backscattering measurements and TEM investigations were performed to study the kind of defects in more detail. The resulting defect profiles are compared with the depth distribution of the nuclear and electronic energy loss which were simulated by TRIM 87. The results show that the remaining defect concentration strongly decreases with increasing implantation energy even if the same energy density is deposited into nuclear processes. We suppose, that the electronic energy loss increases the defect transformation and annealing during implantation at T I = 293 K. The defects in the samples implanted with energies greater than 5 MeV are characterized as point defects, point defect clusters and small dislocation loops; the kind of defects are the same over the whole implantation depth and the existence of amorphous zones can be widely excluded.

Passivation and reactivation of shallow level defects in p-CdTe after low-energy hydrogen implantation

We implanted hydrogen in p-CdTe with very low energy (300 eV/H + ) to minimize self trapping at implantation defects. It is shown by capacitance-voltage (C-V) profiling that hydrogen is mobile in the investigated temperature range between 315 and 360 K during implantation and a complete passivation of acceptor concentrations in the order of 10 16 cm -3 can be achieved. Acceptors with a band-gap level of E = E v + 0.23 eV, which are assigned to cadmium vacancies V Cd as well as acceptors with E = E v + 0.14eV (Cu Cd ) are passivated. Indium-hydrogen pairs or In-V Cd -H complexes were not observed by PAC spectroscopy ( 111 In probe atoms) after hydrogen implantation.

Radiotracer Spectroscopy on Group II Acceptors in GaN

One Be-related donor level in the band gap of GaN was identified by Radiotracer Deep Level Transient Spectroscopy (DLTS) and Thermal Admittance Spectroscopy (TAS). The radioactive isotope Be was implanted into n-type GaN for these experiments. DLTS and TAS spectra were recorded, repeatedly, during the elemental transmutation of Be to Li, whereof the TAS spectra exhibit one level undergoing correlated concentration changes. From this, a relation is deduced between this level at 390 meV below the conduction band edge and a Be-correlated donor state in GaN. Furthermore, the implantation of Be into Mg-doped p-type GaN was observed to enhance the hole concentration significantly. DLTS spectra taken at n-GaN implanted with the radioactive isotope Mg show time-dependent concentration changes that are not related to the characteristic time of the radioactive decay.

Hafnium, cadmium and indium impurities in 4H-SiC observed by perturbed angular correlation spectroscopy

Abstract The annealing behaviour of hafnium impurities in silicon carbide after ion implantation and the formation and stability of complexes of hafnium in 4H-SiC were studied by perturbed angular correlation spectroscopy (PAC) for the first time. Samples of 4H-silicon carbide single crystals were doped with radioactive 181Hf ( t 1 2 = 42.5 d ) and annealed at temperatures of between 600 and 1850 K. After an annealing step at 900 K two axially symmetric electric field gradients (EFGs) were observed oriented along the c-axis of the crystal. Depending on the implantation dose, the fraction of probe atoms exposed to these EFGs increases with the annealing temperature.

Investigation of defects in KTiOPO4 after indium implantation and diffusion

Abstract Perturbed angular correlation spectroscopy (PACS) was used for the first time to study electric field gradients (EFG) in the local electronic environment of indium probe atoms in KTiOPO 4 . Annealing at 1073 K both in oxygen and argon atmosphere leads to the formation of EFG1 in both types of samples and to three additional EFGs in argon annealed samples only. Below 1073 K the annealing behaviour in both cases is nearly identical. High temperature measurements in oxygen atmosphere ranging from room-temperature up to T measure = 1216 K reveal that starting from T measure = 1071 K about 50% of the probe atoms are exposed to one EFG only, namely EFG1. This behaviour is dramatically different from the room-temperature situation. A comparison between samples diffused by 111 In probe atoms and with implanted probes shows that the measured effects are not due to radiation damage.