Fabrication of a Hydrogenated Amorphous Silicon Detector in 3-D Geometry and Preliminary Test on Planar Prototypes

M Menichelli ,Ilaria Cupparo ,Alessandro Rossi ,K Kanxheri ,Giuseppe Maruccio ,C Talamonti ,L Fanò ,A Papi ,A Morozzi ,S Dunand ,L Servoli ,O Hammad Ali ,Silvia Rizzato ,M Caprai ,M Bizzarri ,M Crivellari ,G Cuttone ,F Moscatelli ,Anna Grazia Monteduro ,Giovanni Verzellesi ,Matthew J Large ,Marco Petasecca ,A Scorzoni ,D Passeri ,Anna Paola Caricato ,Giuseppe Antonio Pablo Cirrone ,M Boscardin ,M Ionica ,Nicolas Wyrsch

doi:10.3390/instruments5040032

Abstract

Hydrogenated amorphous silicon (a-Si:H) can be produced by plasma-enhanced chemical vapor deposition (PECVD) of SiH4 (silane) mixed with hydrogen. The resulting material shows outstanding radiation hardness properties and can be deposited on a wide variety of substrates. Devices employing a-Si:H technologies have been used to detect many different kinds of radiation, namely, minimum ionizing particles (MIPs), X-rays, neutrons, and ions, as well as low-energy protons and alphas. However, the detection of MIPs using planar a-Si:H diodes has proven difficult due to their unsatisfactory S/N ratio arising from a combination of high leakage current, high capacitance, and limited charge collection efficiency (50% at best for a 30 µm planar diode). To overcome these limitations, the 3D-SiAm collaboration proposes employing a 3D detector geometry. The use of vertical electrodes allows for a small collection distance to be maintained while preserving a large detector thickness for charge generation. The depletion voltage in this configuration can be kept below 400 V with a consequent reduction in the leakage current. In this paper, following a detailed description of the fabrication process, the results of the tests performed on the planar p-i-n structures made with ion implantation of the dopants and with carrier selective contacts are illustrated.

Highlights

Hydrogenated amorphous silicon (a-Si:H) is a disordered semiconductor obtained from plasma-enhanced chemical vapour deposition (PECVD) of a mixture of Silane (SiH4) and Hydrogen at temperatures of 250-300 °C [1]
The presence of Hydrogen in the mixture has the purpose of passivating most of dangling bonds; in amorphous silicon (a-Si) the density of defects due to DBs is 1019 cm-3 while for a-Si:H this density can be as low as 1015 cm-3
Most of the technological challenges foreseen for the fabrication a 3D detector built on a-Si:H needs to be addressed by the construction of prototypes especially devoted to these purposes

Summary

Introduction

Hydrogenated amorphous silicon (a-Si:H) is a disordered semiconductor obtained from PECVD (plasma-enhanced chemical vapour deposition) of a mixture of Silane (SiH4) and Hydrogen at temperatures of 250-300 °C [1]. The plasma is composed by a doi:10.20944/preprints202107.0556.v1 mixture of silane and hydrogen (ratio of 1 to 1) at temperatures around 200°C and will produce a layer with thickness of around 100 μm After that, both the ohmic and junction columns will be defined and etched using a Deep Reactive Ion Etching (DRIE) apparatus based on Bosh process. A first phase of prototype production should mainly verify if the two doping options, mentioned, can produce efficient junctions for biasing the intrinsic layer and to create an effective charge collection in the construction of a diode that can generate rectification properties. Since p type electrodes should go deep enough in the a-Si:H layer to erase a shallow layer of substrate while n-type electrode should be fully contained in the a-Si:H layer, we would like to verify the possibility of etching p and n type electrodes in one single process exploiting the fact that larger diameter holes have a faster etching rate compared to narrower holes

Leakage current test on option 1

TCAD simulation of a full 3D detector

Conclusions and outlook