J. Sedlmeir

Development of large linear silicon drift detectors for the STAR experiment at RHIC

Abstract Large area linear Silicon Drift Detectors (SDD) are being developed for high energy and relativistic heavy ion collider experiments. SDDs have been proposed for the inner tracking detector in the STAR experiment at the BNL relativistic heavy ion collider to become operational in 1999. The Silicon Vertex Tracker (SVT) will consist of a three layer barrel structure composed of 216 individual detectors, each 6.3 × 6.3 cm 2 . Prototypes, including one-way drift detectors (4.5 × 4.5 cm 2 ) and bi-directional drift detectors (6 × 6 cm 2 ) have been manufactured,and their properties have been studied. Design considerations, as well as test results, are presented in this article. Recent work has focused on minimizing the inactive guard structure area in order to optimize tracking efficiency. Particular attention is given to discussion of parameters that are sensitive to the reduced guard structure area, such as leakage current, maximum voltage and drift non-linearities.

Silicon drift detectors for the STAR/SVT experiment at RHIC

Large area linear Silicon Drift Detectors (SDD) were developed to be used in the Silicon Vertex Tracker (SVT) of the STAR experiment at the BNL relativistic heavy ion collider (RHIC). The SDD is in its final design and has been submitted for large scale production. Test results show that the detector exhibits excellent position resolution and low noise. A special characterization procedure was developed to test detector wafers in order to select good detectors for the SVT. Recently, 15 STAR/SVT SDDs were assembled as a tracking device in a BNL-AGS heavy ion experiment (E896). It is the first tracking application of these detectors and their corresponding front-end electronics in an experimental environment. Preliminary results indicating good detector performance are shown and discussed in this paper.

Studies of dynamics of electron clouds in STAR silicon drift detectors

Abstract The dynamics of electrons generated in silicon drift detectors was studied using an IR LED. Electrons were generated at different drift distances. In this way, the evolution of the cloud as a function of drift time was measured. Two methods were used to measure the cloud size. The method of cumulative functions was used to extract the electron cloud profiles. Another method obtains the cloud width from measurements of the charge collected on a single anode as a function of coordinate of the light spot. The evolution of the electron cloud width with drift time is compared with theoretical calculations. Experimental results agreed with theoretical expectations.

Electron injection in semiconductor drift detectors

Abstract We report on the injection of electrons from surface structures of Silicon Drift Detectors into the bulk of the detector for calibration purposes. Also, with these injector structures, detection of magnetic field components perpendicular to the detector’s surface is possible. Implanted line and dot injectors along with MOS injectors are discussed. Studies of lateral uniformity of injection, biasing of injectors to facilitate injection and dot injection are discussed.

Transport properties of electrons in silicon drift detectors measured in large magnetic fields

Abstract A 45 × 45 mm rectangular n-type Silicon Drift Detector was studied in magnetic fields ranging from 0 to 4.7 T and for drift fields from 200 to 380 V/cm. Transport properties of electrons in silicon (Hall mobility, drift mobility and magnetoresistance) were determined by pulsing the detector with a Nd:YAG laser at different drift lengths and measuring both the transverse deflections of the signal and the increases in drift time versus an applied magnetic field. The width of the signal in both the drift and anode direction increased with magnetic field. The magnetic field was aligned parallel and normal to the drift direction. The detector was found to operate well for conditions expected in future experiments at the RHIC collider and experiment E896 at Brookhaven National Laboratory.

The silicon drift vertex detector for the STAR experiment at RHIC

Abstract The current status of the STAR Silicon Vertex Tracker (SVT) is presented. The performance of the Silicon Drift Detectors (SDD) is discussed. Results for a recent 15 layer SDD tracker which prototypes all components of the SVT are presented. The enhanced physics capabilities of the STAR detector due to the addition of the SVT are addressed.

Two dimensional studies of dynamics of electron clouds in silicon drift detectors

The dynamics of electrons generated in silicon drift detectors is studied using an IR LED. Electrons were generated at different drift distances. In this way the evolution of the cloud in anode and drift directions as a function of drift time was measured. For the anode direction the method of cumulative functions was used to extract the electron cloud profiles. The cloud width was obtained also from measurements of the charge collected on a single anode as a function of the coordinate of the light spot. We present the first report of the experimental measurements of the cloud width in the drift direction extracted from signal waveforms. The evolution of the electron cloud width with drift time is compared with theoretical calculations. Theoretical expectations agree with our experimental results.

Measurement of two particle resolution in silicon drift detectors

A study resolving two hits in a 45/spl times/45 mm rectangular n-type Silicon Drift Detector is presented as a function of drift field using a pulsed Nd:Yag laser. The data are analyzed under the assumption of the general form of a Gaussian distribution in two variables (including correlations). The two hit resolving power degrades with drift distance. As the two electron clouds approach each other their correlation coefficients are shown to increase and be anti-correlated. Arguments for optimal two hit resolution versus drift field are presented. A simple method to determine whether electron cloud distributions arise from multiple overlapping hits or single hits is demonstrated. Practical implications for analyzing data from high occupancy experiments such as STAR at the RHIC collider are discussed.

Double particle resolution in STAR silicon drift detectors

The inner tracking detector of the STAR experiment at the BNL Relativistic Heavy Ion Collider will consist of a three layer barrel structure of 216 silicon drift detectors. Calculations of the two-hit resolution achievable for these detectors are presented in this article. The effects on two-hit resolution of the electronics response function, frequency of signal digitization and noise level are discussed.

Probe station testing of large area silicon drift detectors

Probe stations for STAR Silicon Drift Detectors testing were developed and built at BNL and Ohio State University. A throughput of a wafer per day per probe station was reached. Testing procedure and probe station design criteria are discussed.