Improved electroless platinum contacts on CdZnTe X- and γ-rays detectors

Abstract

platinum is a promising candidate for the realization of blocking electrical contacts on cadmium-zinctelluride (cdZnte or cZt) radiation detectors. However, the poor mechanical adhesion of this metal often shortens the lifetime of the final device. In this work, a simple and effective procedure to obtain robust platinum contacts by electroless deposition is presented. Microscopical analysis revealed the final thickness and composition of the contact layer and its adhesion to the bulk crystal. The blocking nature of the Pt-CdZnTe junction, essential to obtain low noise devices, was confirmed by current-voltage measurements. the planar pt-cdZnte-pt detectors showed good room temperature spectroscopic performance with energy resolution of 4% (2.4 keV) and 3% (3.7 keV) FWHM at 59.5 and 122.1 keV, respectively. Finally, we showed, for the first time, that platinum contacts allow the estimation of the carrier lifetime and mobility of both holes and electrons by using current transient measurements. This demonstrated the optimal hole extraction capability of such contacts. CdTe and CdZnTe (CZT) have proven to be excellent materials for room temperature X-ray and gamma-ray detectors and they are gradually replacing other sensing systems in many applications. Electrical contacts on such detectors need to be customised according to the final purpose of the device and engineered depending on the properties of the starting material such as work function and bulk resistivity. A great interest has been addressed to platinum metal contacts 1-3 because Pt work function (~ 5.6 eV) leads to the formation of a high Pt-CZT Schottky barrier which limits the carrier injection and thus the leakage current. This is the reason why blocking contacts are usually adopted to realize high-resolution spectrometers 4. Electroless deposition technique is vastly used to deposit contacts on II/VI materials. The reason lies in its simplicity since no specific or expensive laboratory equipment is required. This method consists in the spontaneous reaction of the metal in salt form dissolved in a proper solvent with the detector material. The reaction takes place without the use of any external electric power and allows to realize chemically stable and reproducible contacts. Moreover, the oxide formation at the metal/semiconductor interface is minimised since contacts are realised immediately after the polishing step, hence reducing the air exposition of the highly reactive surface. This is crucial to reduce the effect of the oxide layer on the leakage current and charge collection efficiency. Lastly, fine tuning of electroless deposition parameters allows to control the final quality of the metallic layer in term of thickness and homogeneity. In this work, Pt contacts have been deposited by means of a electroless deposition technique based on alcoholic solution. The CdZnTe detectors have been realised and characterised thorough mechanical, structural, electrical, and spectroscopic analysis. This study is focused on explaining the role of the metal/se...

Effect of Ar Plasma Treatment on the Interface and Performance of CdZnTe Detectors

“…The reverse current density J, as a function of the reverse bias voltage V, can be expressed by Equation (1). When the voltage was greater than 100 V, the thermionic emission mechanism dominated, and the expression of reverse current density J can be simplified as follows [24]…”

“…The reverse current density J , as a function of the reverse bias voltage V , can be expressed by Equation (1). When the voltage was greater than 100 V, the thermionic emission mechanism dominated, and the expression of reverse current density J can be simplified as follows [ 24 ] $$$$\begin{equation}J = {C_1}\exp \left( {\frac{{q{C_2}V}}{{kT}}} \right)\end{equation}$$$$with $$$$\begin{equation}{C_1} = {\theta _{\rm{n}}}{A^*}{T^2}\exp \left( { - \frac{{{\varphi _{{\rm{B}}0}}}}{{kT}}} \right),\;{C_2} = 1 - \frac{{{\varepsilon _{\rm{i}}}}}{{{\varepsilon _{\rm{i}}} + 2q{\delta _{\rm{i}}}{D_{\rm{s}}}}}\end{equation}$$$$…”

Electroless Metallization of the Elements: Survey and Progress

“…We note here that CdTe and related materials have also found use as substrates in galvanic replacement reactions. Several examples of galvanic deposition of metals, such as Pt, Ru, and Mo and W and their oxides, onto CdTe and CdZnTe have already been described in other sections of this article ( i.e ., Platinum section, Ruthenium section, and the Molybdenum and Tungsten section).…”

“…Pt IV is reduced to Pt II and then Pt 0 by Cd oxidation to Cd II and Te oxidation to TeO 2 . Bettelli et al 391 have investigated Pt contact adhesion for Pt-CdZnTe composites used as high sensitivity gamma and X-ray detectors. Pt deposited by galvanic displacement of Cd by PtCl 6 2− in water suffers from poor adhesion and uniformity.…”

Emerging II-VI wide bandgap semiconductor device technologies

“…Specifically, Copper Cu (thermal annealing at 200 °C for 1 h) for CdS [36]. Platinum for CdZnTe [37] Sb 2 Te 3 for CdTe [38] HgTe for p-CdHgTe and CdTe [39]. In [40] and In-Ga (with thermal annealing at 400-475 °C) for ZnS [41] regrowth and in situ Al (at 475 °C) [42] ZnSe 1−x Te x grading [43] and In (at 475 °C) for ZnSe [44] liquid alloys of In(Hg) or In(Ga) for ZnS x Se 1−x [45] Au/Pt/Pd or Au/Mo/Pd stack for p-ZnTe [46] found as potential for facilitating Ohmic contacts.…”