Transient Current Technique Measurements Research Articles

TCT investigation of the one-sided depletion of low-temperature covalently bonded silicon sensor P-N diodes

In the context of particle detectors, low-temperature covalent wafer-wafer bonding allows for integration of high-Z materials as absorbing layers with readout chips produced in standard CMOS processes. This enables for instance the fabrication of novel highly efficient X-ray imaging sensors. In order to investigate the effects of the covalent bonding on the signal generated in such sensors, wafer-wafer bonded silicon-silicon P-N pad diodes have previously been produced. The behaviour of these test samples is being investigated with transient current technique (TCT) measurements. In this paper we present an overview of the TCT setup as well as a custom sandwich-type sample holder used for these measurements. A review of the results presented in a previous paper shows, that the bonded P-N structures show a highly asymmetric depletion behaviour under reverse bias. IR edge TCT measurements confirm that only the P-side of the samples is being depleted.

Characterization of magnetic Czochralski silicon devices with aluminium oxide field insulator: effect of oxygen precursor on electrical properties and radiation hardness

Aluminium oxide (Al2O3) has been proposed as an alternative to thermal silicon dioxide (SiO2) as field insulator and surface passivation for silicon detectors, where it could substitute p-stop/p-spray insulation implants between pixels due to its negative oxide charge, and enable capacitive coupling of segments by means of its higher dielectric constant.Al2O3 is commonly grown by atomic layer deposition (ALD), which allows the deposition of thin layers with excellent precision.In this work, we report the electrical characterization of single pad detectors (diodes) and MOS capacitors fabricated on magnetic Czochralski silicon substrates and using Al2O3 as field insulator. Devices are studied by capacitance-voltage, current-voltage, and transient current technique measurements. We evaluate the influence of the oxygen precursors in the ALD process, as well as the effect of gamma irradiation, on the properties of these devices. We observe that leakage currents in diodes before the onset of breakdown are low for all studied ALD processes. Charge collection as measured by transient current technique (TCT) is also independent of the choice of oxygen precursor. The Al2O3 films deposited with O3 possess a higher negative oxide charge than films deposited by H2O, However, in diodes a higher oxide charge is linked to earlier breakdown, as has been predicted by simulation studies. A combination of H2and O3 precursors results in a good compromise between the beneficial properties provided by the respective individual precursors.

Charge carrier properties of single-crystal CVD diamond up to 473 K

The drift behavior of charge carriers, generated by α-particles of a reference 241Am-source, in electronic grade, single crystal chemical vapor deposition (scCVD) diamond was investigated by the transient current technique (TCT) from room temperature up to ≈473K. Furthermore, the α-spectroscopic behavior was analyzed in terms of charge collection and spectroscopic resolution for the same temperature range. All conducted measurements revealed complete charge collection up to the maximum temperature. The electron–hole-pair creation energies were derived from the TCT as well as from the spectroscopic measurements. The herein presented results imply that high temperature α-spectroscopy with diamond-based semiconductor solid state detectors, using presently available scCVD sensor substrates, is feasible at least up to 473K. Only at the highest applied temperature, the conducted TCT measurements showed distorted signal traces, indicating a uniform positive space charge built-up.

TCT measurements with slim edge strip detectors

Transient current technique (TCT) measurements with focused laser light on miniature silicon strip detectors (n+-type strips on p-type bulk) with one inactive edge thinned to about 100µm using the Scribe-Cleave-Passivate (SCP) method are presented. Pulses of focused IR (λ=1064nm) laser light were directed to the surface of the detector and charge collection properties near the slim edge were investigated. Measurements before and after irradiation with reactor neutrons up to 1MeV equivalent fluence of 1.5×1015neq/cm2 showed that SCP thinning of detector edge does not influence its charge collection properties.TCT measurements were done also with focused red laser beam (λ=640nm) directed to the SCP processed side of the detector. The absorption length of red light in silicon is about 3µm so with this measurement information about the electric field at the edge can be obtained. Observations of laser induced signals indicate that the electric field distribution along the depth of the detector at the detector edge is different than in the detector bulk: electric field is higher near the strip side and lower at the back side. This is a consequence of negative surface charge caused by passivation of the cleaved edge with Al2O3. The difference between bulk and edge electric field distributions gets smaller after irradiation.

Development of Radiation Hard Particle Detectors Made of Czochralski Grown Silicon

Tracking detectors to be used in the future high-luminosity particle physics experiments have to be simultaneously radiation hard and cost e cient. Magnetic Czochralski silicon wafers can be grown with su ciently high resistivity (several kΩ cm) and well-controlled high oxygen concentration. Signi cant research and development activity aiming to develop particle detectors made of high resistivity magnetic Czochralski silicon has been ongoing during the past decade. Beam test results presented in this paper show that n-type magnetic Czochralski silicon strip detectors can be operated with acceptable signal-to-noise ratio at least up to a 1 MeV neutron equivalent (neq) uence of 1 × 10 cm−2. The improved radiation hardness, compared to more commonly used oat zone silicon, can be explained by the more bene cial electric eld distribution inside the detector bulk. We have demonstrated a S/N of > 10 for full-size strip detectors attached to readout electronics at a uence of 1 × 10 neq/cm. These ndings are supporting our transient current technique measurements.

Study on [formula omitted] thick n- and p-type epitaxial silicon sensors irradiated with 24 GeV/ c protons and 1 MeV neutrons

A study on 150 μ m epitaxial (EPI) n- and p-type silicon diodes irradiated with neutrons up to 8 × 10 15 n / cm 2 and protons up to 1.7 × 10 15 p / cm 2 has been performed by means of CV/IV, charge collection efficiency (CCE) and transient current technique (TCT) measurements. It is found that the effective space charge density increases three times faster after proton than after neutron irradiation with a slightly higher effective space charge generation rate for n-type material compared to p-type material. A drop in charge collection efficiency already at fluences of 1 × 10 12 n eq / cm 2 can be seen in n-type material, but is absent in p-type material. TCT measurements show space charge sign inversion from positive to negative charge in n-type material after neutron irradiation and from negative to positive space charge in p-type material after proton irradiation. No difference was found in the response of diodes manufactured by different producers out of the same wafer material.

TCT and test beam results of irradiated magnetic Czochralski silicon (MCz-Si) detectors

Pad and strip detectors processed on high resistivity n-type magnetic Czochralski silicon (MCz-Si) were irradiated to several different fluences with protons. The pad detectors were characterized with the transient current technique (TCT) and the full-size strip detectors with a reference beam telescope and a 225 GeV muon beam. The TCT measurements indicate a double junction structure and space charge sign inversion in MCz-Si detectors after 6 × 10 14 1 MeV n eq / cm 2 fluence. In the beam test a signal-to-noise ( S/ N) ratio of 50 was measured for a non-irradiated MCz-Si sensor, and a S/ N ratio of 20 for the sensors irradiated to the fluences of 1 × 10 14 1 and 5 × 10 14 1 MeV n eq / cm 2 .

Characterization of [formula omitted] thick epitaxial silicon detectors from different producers after proton irradiation

Epitaxial (EPI) silicon has recently been investigated for the development of radiation tolerant detectors for future high-luminosity HEP experiments. A study of 150 μ m thick EPI silicon diodes irradiated with 24 GeV / c protons up to a fluence of 3 × 10 15 p / cm 2 has been performed by means of Charge Collection Efficiency (CCE) measurements, investigations with the Transient Current Technique (TCT) and standard CV / IV characterizations. The aim of the work was to investigate the impact of radiation damage as well as the influence of the wafer processing on the material performance by comparing diodes from different manufacturers. The changes of CCE, full depletion voltage and leakage current as a function of fluence are reported. While the generation of leakage current due to irradiation is similar in all investigated series of detectors, a difference in the effective doping concentration can be observed after irradiation. In the CCE measurements an anomalous drop in performance was found even for diodes exposed to very low fluences ( 5 × 10 13 p / cm 2 ) in all measured series. This result was confirmed for one series of diodes in TCT measurements with an infrared laser. TCT measurements with a red laser showed no type inversion up to fluences of 3 × 10 15 p / cm 2 for n-type devices whereas p-type diodes undergo type inversion from p- to n-type for fluences higher than ≈ 2 × 10 14 p / cm 2 .

Czochralski silicon detectors irradiated with [formula omitted] and 10 MeV protons

We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with 24 GeV / c and 10 MeV protons. Samples were characterized with Capacitance-Voltage measurements (CV), Transient Current Technique (TCT) and secondary electron backscattering recorded by Scanning Electron Microscope (SEM). We present the evolution of the effective doping concentration as a function of irradiation fluence as well as the introduction rate of negative space charge, β -parameter. According to these measurements, we found that Cz-Si is more radiation hard than Fz-Si. Both TCT and SEM measurements indicated that Space Charge Sign Inversion (SCSI) occurred in the heavily irradiated Fz-Si and in the Cz-Si irradiated with 10 MeV protons. However, the SCSI did not take place in Cz-Si irradiated with 24 GeV / c protons even after high irradiation fluence.

P/sup +//n/sup -//n/sup +/ cz-Si detectors processed on p-type boron-doped substrates with thermal donor induced space charge sign inversion

We have processed pad detectors on high-resistivity p-type Cz-Si wafers. The resistivity of the boron-doped silicon is approximately 1.8 k/spl Omega/ cm after the crystal growth. The detector processing was carried out using the common procedure for standard n-type wafers, to produce p/sup +//p/p/sup -//n/sup +/ detector structures. During the last process step, i.e., sintering of aluminum electrode, the p-type bulk was turned to n-type through generation of thermal donors (TD). This way, high oxygen concentration p/sup +//n/sup -//n/sup +/ Cz-Si detectors were realized with low temperature process. The full depletion voltage of detectors could be tailored between wide range from 30 V up to close 1000 V by changing heat treatment at 400/spl deg/C-450/spl deg/C duration from 20 to 80 min. The space charge sign inversion (SCSI) in the TD generated devices (from p/sup +//p/sup -//n/sup +/ to p/sup +//n/sup -/(inverted)/n/sup +/) has been verified by transient current technique measurements. The detectors show very small increase of full depletion voltage after irradiations with 24 GeV/c protons up to 5*10/sup 14/ p/cm/sup 2/.