Charge Collection Efficiency Profiles Research Articles

Study of depth-dependent charge collection profiles in irradiated pad diodes

In this work, charge collection profiles of non-irradiated and irradiated 150µm thick p-type pad diodes were measured using a 5.2GeV electron beam traversing the diode parallel to the readout electrode. Four diodes were irradiated to 1MeV neutron equivalent fluences of 2, 4, 8, and 12 × 1015cm−2 with 23MeV protons. The Charge Collection Efficiency profiles as a function of depth are extracted by unfolding the data. The results of the measurements are compared to the TCAD device simulation using three radiation damage models from literature which were tuned to different irradiation types and fluences.

Depth-dependent charge collection profile of pad diodes

The collected charge of two pad diodes is measured along the diode width using a 5.2GeV electron beam at the DESY II beam test facility. The electron beam enters parallel to the readout electrode plane and perpendicular to the edge of the diode. The position of the electron beam is reconstructed by three planes of an EUDET-type telescope. An in-situ procedure is developed to align the diode surface parallel to the electron beam. The result of these measurements is the charge collection efficiency profile as a function of depth for each diode. For a non-irradiated diode, the charge profile is uniform as a function of the beam position for bias voltages above the full-depletion, as expected. For the irradiated diode, the charge profile is non-uniform and changes as a function of bias voltage.

Monte Carlo analysis of a lateral IBIC experiment on a 4H-SiC Schottky diode

The transport properties of a 4H-SiC Schottky diode have been investigated by the ion beam induced charge (IBIC) technique in lateral geometry through the analysis of the charge collection efficiency (CCE) profile at a fixed applied reverse bias voltage.The cross section of the sample orthogonal to the electrodes was irradiated by a rarefied 4MeV proton microbeam and the charge pulses have been recorded as function of incident proton position with a spatial resolution of 2μm.The CCE profile shows a broad plateau with CCE values close to 100% occurring at the depletion layer, whereas in the neutral region, the exponentially decreasing profile indicates the dominant role played by the diffusion transport mechanism.Mapping of charge pulses was accomplished by a novel computational approach, which consists in mapping the Gunn’s weighting potential by solving the electrostatic problem by finite element method and hence evaluating the induced charge at the sensing electrode by a Monte Carlo method. The combination of these two computational methods enabled an exhaustive interpretation of the experimental profiles and allowed an accurate evaluation both of the electrical characteristics of the active region (e.g. electric field profiles) and of basic transport parameters (i.e. diffusion length and minority carrier lifetime).

Lateral IBIC characterization of single crystal synthetic diamond detectors

AbstractIn order to evaluate the charge collection efficiency (CCE) profile of single‐crystal diamond devices based on a p‐type/intrinsic/metal configuration, a lateral Ion Beam Induced Charge (IBIC) analysis was performed over their cleaved cross sections using a 2 MeV proton microbeam. CCE profiles in the depth direction were extracted from the cross‐sectional maps at variable bias voltage. IBIC spectra relevant to the depletion region extending beneath the frontal Schottky electrode show a 100% CCE, with a spectral resolution of about 1.5%. The dependence of the width of the high efficiency region from applied bias voltage allows the constant residual doping concentration of the active region to be evaluated. The region where the electric field is absent shows an exponentially decreasing CCE profile, from which it is possible to estimate the diffusion length of the minority carriers by means of a drift–diffusion model. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A grazing angle technique to measure the charge collection efficiency for CMOS active pixel sensors

Abstract Recently, CMOS Monolithic Active Pixels Sensors have become strong candidates as pixel detectors to be used in high energy physics experiments. A very good spatial resolution and an excellent detection efficiency could be obtained with these detectors. Beside spatial resolution and detection efficiency, an important parameter to be investigated is the charge collection efficiency (CCE) as a function of the distance from the detector surface. In this paper a new approach to measure the CCE profile by means of ionizing particles is proposed.

Characterization of charge carrier collection in a CdZnTe Frisch collar detector with a highly collimated [formula omitted] source

A 4.7 ×4.7×9.5 mm 3 CdZnTe Frisch collar device was characterized through probing the device with a highly collimated Cs 137 662 keV gamma ray source. In a systematic series of experiments, the detector was probed along the length and width with a Cs 137 gamma ray source using a 43.0 mm long Pb-collimator with a 0.6 mm circular hole. The detector was probed along the central line under different operating voltages of 1200, 1000, 800, 600 and 400 V. The experimental results correlated well to charge collection calculations for a modeled device with the same size and operating conditions. It was proved that, unlike the planar configuration, the charge collection efficiency profile along the length of Frisch collar device is considerably improved. The CdZnTe raw materials for this study were acquired from Redlen Technologies, and the Frisch collar device was fabricated and characterized at S.M.A.R.T. Laboratory at Kansas State University.

Charge collection characteristics of Frisch collar CdZnTe gamma-ray spectrometers

A collimated 198Au source was used to determine the charge collection efficiency (CCE) at several locations along the length of a 3.4×3.4×5.5 mm 3 CdZnTe bar detector, both in planar configuration and with Frisch collars of varying length. For each configuration, a 0.50-mm-long region spanning the width of the device was irradiated with 411-keV gamma rays produced by a neutron-activated gold foil. Irradiation began at the cathode and stepped in 0.50-mm steps toward the anode, with a spectrum being collected at each location. By observing the channel location of the full-energy peak in each collected spectrum, an average CCE was determined for each irradiated region. The CCE was found to vary nearly linearly along the length of the device in the planar configuration, starting at a peak value of 89% and dropping to a minimum measured value of 26% near the anode. The addition of a Frisch collar covering the entire length of the crystal greatly altered the CCE profile, which remained near 87% for approximately two-thirds of the length, then sharply dropped near the anode. Results were confirmed by theoretical models. Further CCE mapping was also completed for devices with Frisch collars of various lengths. Those results are reported as well.

Measurement of charge collection profiles in irradiated silicon diodes by lateral IBIC technique

The control of the carrier lifetime profile in semiconductor power devices is of fundamental importance to optimize device parameters. With respect to traditional technologies such as diffusion of metallic impurities, light ion irradiation at low doses provides precise spatial localization of defects acting as carrier traps and recombination centres. Hence, the generation of suitable lifetime profiles obtained by controlling ion fluence and energy allows the reduction of turn-off times and switching losses in power electronic devices. In order to characterise the effects of ion irradiation on carrier lifetime profiles, we have used the ion beam induced charge collection (IBIC) technique in lateral geometry to measure charge collection efficiency (CCE) profiles in silicon p+/n/n+ diodes under different applied bias conditions before and after a frontal 6.5 MeV He++ ion implantation at a total fluence of 2 × 10 12 ions/cm 2. After the irradiation, the profile shows a clear drop of charge collection efficiency which occurs at the end of the ion range. The formalism based on Shockley–Ramo–Gunn’s theorem was applied to interpret the CCE profiles in both virgin and irradiated samples and to assess the free carrier lifetime profile modification following the radiation damage.

Lateral IBIC analysis of GaAs Schottky diodes

Charge collection efficiency (CCE) profiles of a semi-insulating (SI) gallium arsenide LEC (Liquid Encapsulated Czochralski) Schottky diode have been investigated by lateral Ion Beam Induced Charge collection (IBIC) technique. A focussed 2.4MeV proton microbeam was scanned over the cleaved surface of a SI-GaAs diode and the charge collection efficiency was evaluated as a function of the ion beam position at different bias voltages.By fitting the CCE profiles with the equations derived by the Shockley–Ramo–Gunn’s theorem, drift lengths of electrons and holes were obtained. Experimental results are consistent with previous OBIC (Optical Beam Induced Current) and SP (Surface Potential) measurements and confirm the model based on the formation of a Mott barrier due to the enhanced electron capture cross section in high field conditions.

Lateral micro-ion beam induced charge characterization of chemical vapor deposition diamond

A lateral micro-ion beam induced charge technique has been used to obtain the charge collection efficiency (CCE) profiles at different biases applied on the growth electrode of chemical vapor deposition (CVD) diamond. A new linear model, only related to characteristic parameters (mobility×lifetime product) of CVD diamond, was reasonably proposed and checked by fitting the CCE profile. The results confirm that: (1) this CVD diamond is similar to a n–p junction film with bulk volume p type on the substrate side at the positive bias applied on the growth side; (2) in the case of negative bias, space charge on both sides may arise from donors/acceptors of the film and electrons/holes injected from the growth/substrate side, but in the middle no space charge exists due to the electron–hole neutralization.

Investigation on the electric field profile in CdTe by ion beam induced current

The charge collection efficiency profile along the thickness of a CdTe detector was measured for first time by using a proton microbeam and a polished cross-section of the devices. Different samples were investigated and tests were carried out along different lines from cathode to anode, with different biases and polarities, and with different shaping times. The effects of all these parameters are evident in the experimental curves. By fitting these curves, the behaviour of the drift length for electrons and holes is obtained, if a constant ratio between them is assumed. If the mobilities and trapping times are uniform, the electric field profile is obtained. The profile has a minimum at the anode and a maximum towards the cathode, at least for large bias voltage.

Effects of the Concentration of Ga on Junction Formation in Thin-film ZnO/CdS/CuInXGal-XSe2 /Mo Photovoltaic Devices

AbstractCharge-collection microscopy (CCM)—commonly known as electron-beam-induced current [EBIC] microscopy—in a scanning electron microscope (SEM) was used to obtain charge-collection efficiency profiles of cleaved thin-film ZnO/CdS/CuInXGal-XSe2/Mo photovoltaic devices on glass substrates, with x varied between 0 and 100%. We observed considerable variation in the EBIC peak position, the uniformity (between and within devices), and overall charge-collection profile of the junction as a function of Ga concentration. Whereas using only CuInSe2 (CIS) absorber material results in a rather wide and buried junction in the CIS, the systematic addition of Ga to the p-CuInSe2 matrix affects the conductivity type of the material, thereby creating an increasingly abrupt, uniform, and shallow junction near the heteroface. Although the substitution of Ga for In improves overall device performance up to ∼ X=25% and the Voc continues to improve, the Jsc, FF, and device efficiency degrade with additional Ga.