Characterizing Novel Indium Phosphide Pad Detectors with Focused X-ray Beams and Laboratory Tests

TL;DR

This work assesses Indium Phosphide:Fe pad sensors as a thin-film alternative for scalable, low-r radiation-length tracking detectors in high-energy physics. It combines electrical characterization (IV/CV) with micro-focused X-ray beam tests at CLS and DLS to map both inter-device and intra-device uniformity under ionizing radiation. The results show symmetric IV behavior with no breakdown up to standard voltages, a breakdown threshold near ±1010 V, and generally low device-to-device leakage variation except for a small cluster of high-current devices; X-ray tests reveal mainly uniform responses with edge-field enhancements and some localized defects. The study demonstrates the viability of InP-based thin-film detectors for tracking applications and highlights design and bonding improvements (e.g., thicker top metal, additional guard rings) to mitigate edge effects and wiring-induced damage, justifying further development of this material system for future large-area detectors.

Abstract

Future tracking systems in High Energy Physics experiments will require large instrumented areas with low radiation length. Crystalline silicon sensors have been used in tracking systems for decades, but are difficult to manufacture and costly to produce for large areas. We are exploring alternative sensor materials that are amenable to fast fabrication techniques used for thin film devices. Indium Phosphide pad sensors were fabricated at Argonne National Lab using commercially available InP:Fe 2-inch mono-crystal substrates. Current-voltage and capacitance-voltage characterizations were performed to study the basic operating characteristics of a group of sensors. Micro-focused X-ray beams at Canadian Light Source and Diamond Light Source were used to study the response to ionizing radiation, and characterize the uniformity of the response for several devices. The results show a high degree of performance uniformity in our evaluations, both within a device and between the 48 tested devices. This motivates further studies into thin film devices for future tracking detectors.

Figures (27)

• Figure 1: Frontside profile photos of typical devices, one with device solid central pad metallization (left) and another containing a central hole in the pad (right)
• Figure 2: Edge profile photos of a typical device
• Figure 3: A stackup diagram of InP devices architecture.
• Figure 4: Shadow masks used to pattern the frontside conductors of single-pad devices. The left image shows the "no-hole" (NH) conductor pattern, while the right image shows the "hole" (H) conductor pattern. Both patterns contain a central pad and guard ring, save for the 150 $\mu$m diameter hole in the H central pad.
• Figure 5: IV curves of the full set of 48 InP devices. Each device corresponds to a distinct colored line. The majority of IV curves span from -600 V to 600 V. All IV curves above were recorded with a floating guard ring. In the second figure, IV measurements are shown from 1-600 V with logarithmic horizontal and vertical axes, with current density and field strength replacing current and voltage respectively. The current density and field strength are calculated assuming the architecture of an ideal geometry, using the central pad area for the current normalization.