HgCdTe Detector Substrate Removal Iodine Passivation
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Solution Overview
Problem
Conventional methods for eliminating the CdZnTe growth substrate from electromagnetic radiation detectors, particularly those made of HgCdTe, result in insufficient selectivity and residual composition gradients, leading to recombination of photocarriers and reduced sensitivity in the visible and near-infrared ranges due to the presence of recombinant centers on the surface.
Innovation Solution
A method involving mechanical or chemical-mechanical polishing followed by an iodine treatment using an acidic aqueous solution, such as KI/I2/HBr, to form a stable iodine surface film that passivates the surface, eliminating recombinant centers and maintaining the composition gradient, thereby preventing photocarrier recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mechanical or chemical-mechanical polishing is used to eliminate the CdZnTe growth substrate, then the substrate thickness is reduced, but residual composition gradients remain causing photocarrier recombination
Solution Approach 1:
An intermediary layer of HgTe is introduced between the CdZnTe substrate and the HgCdTe detection layer. This intermediary layer serves as a buffer that prevents direct interaction between the substrate and detection layer, eliminating the harmful composition gradient while maintaining structural integrity during the substrate elimination process.
Solution Approach 2:
The detection circuit is segmented into distinct layers: the HgCdTe detection layer, the intermediary HgTe layer, and the CdZnTe substrate. This segmentation allows independent treatment of each layer, enabling selective elimination of the substrate while preserving the detection layer's compositional integrity and photocarrier collection efficiency.
2Ease of manufacture
If chemical etching is used to remove the CdZnTe substrate, then selectivity between CdZnTe and HgCdTe is achieved, but selectivity deteriorates when cadmium composition approaches x=0.5
Solution Approach 1:
The HgTe intermediary layer acts as a chemical buffer that protects the HgCdTe detection layer from direct exposure to etching solutions. This intermediary layer has different etching characteristics than HgCdTe, allowing selective removal of the CdZnTe substrate while preserving the detection layer's precise composition gradient.
3Reliability
If the CdZnTe substrate is eliminated to improve near-infrared and visible detection, then sensitivity to these wavelengths increases, but recombinant centers on the surface cause photocarrier recombination
Solution Approach 1:
The HgTe intermediary layer serves as a protective intermediary between the CdZnTe substrate and the HgCdTe detection layer. When the substrate is eliminated, the HgTe layer remains as a passivating interface that eliminates surface recombination centers, thereby maintaining high detection sensitivity without the harmful effects of surface recombination.
Solution Approach 2:
The HgTe intermediary layer, which initially appears as an additional structural element, actually converts the potentially harmful substrate-detection layer interface into a beneficial passivated surface. This intermediary structure transforms what would be a source of recombination into a protective feature that enhances photocarrier collection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The iodine treatment effectively neutralizes recombinant centers on the HgCdTe surface, enhancing detector sensitivity by allowing photocarriers from short wavelengths to be collected, reducing absorption issues, and maintaining stability over temperature and time.
Implementation Method 1
an acidic aqueous solution of KI/I2/HBr or of HI/I2... leads to the formation of a very thin surface film of elemental iodine, directly bridged to the surface and stable over time and temperature
Implementation Method 2
an alloy corresponding to the generic formula HgCdTe, a material well known for absorbing electromagnetic radiation located in the infrared... transforming electromagnetic radiation into an electrical signal
Implementation Method 3
the Cd(Zn)Te substrate absorbs the incident radiation in the near infrared or visible wavelength ranges, so that the detected signal is reduced
Implementation Method 4
a cadmium composition gradient between the active layer Hg (1 - x) Cd x Te and the substrate is created... the residual cadmium composition gradient and the associated conduction and valence band potential gradients are sufficient to drive the photocarriers away from the back face
Data Source
Figure 1a~1c
AI summary
The method for removing a cadmium zinc telluride growth substrate of a circuit for detecting electromagnetic radiation such as infrared or visible radiations, comprises subjecting the growth substrate to a mechanical polishing or chemical mechanical polishing step or an etching step to reduce its thickness to produce an interface zone between a material of the detection circuit and the growth substrate, and subjecting the interface to an iodine treatment. The iodine is present in the molecular form in solution comprising water and methanol as a solvent. The method for removing a cadmium zinc telluride growth substrate of a circuit for detecting electromagnetic radiation such as infrared or visible radiations, comprises subjecting the growth substrate to a mechanical polishing or chemical mechanical polishing step or an etching step to reduce its thickness to produce an interface zone between a material of the detection circuit and the growth substrate, and subjecting the interface to an iodine treatment. The iodine is present in the molecular form in solution comprising water and methanol as a solvent. The iodine treatment is performed in an acid medium preceded by deoxidizing action of the surface area of variation residual composition (5') after the mechanical polishing or chemical-mechanical polishing step or etching step, where the deoxidizing action is carried out by subjecting the interface zone to a bath including composition, and is performed by immersing a detector resulting from mechanical polishing and/or chemical-mechanical steps and/or etching step in the bath. The circuit includes a radiation detection layer made of mercury cadmium telluride (Hg ( 1 - x )Cd xTe) that is obtained by liquid or vapor phase epitaxy or by molecular beam epitaxy, and is hybridized on a read circuit. The growth substrate is made of a monocrystalline semiconductor in which a cadmium telluride lattice parameter adaptation layer is deposited. The adaptation layer has a thickness of several micrometers. The interface zone is subjected to chemical etching to remove the residual thickness of the growth substrate prior to subjecting the interface zone to the iodine treatment and after the step of mechanical polishing or chemical-mechanical polishing or etching step.