In-situ Laser Annealing of Te Precipitates in CdZnTe Growth
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The formation of large Te precipitates in as-grown CdZnTe boules due to stoichiometry deviations during growth leads to dislocation clusters, surface defects, and voids in epilayers, which can short circuit Focal Plane Arrays and result in blind pixels, and existing annealing methods fail to effectively eliminate these inclusions while maintaining high electrical resistivity and improving substrate quality.
Innovation Solution
A method involving localized in-situ annealing using a laser mounted on the crystal growth furnace to melt and thermo-migrate Te precipitates at the crystal-melt interface, reducing unwanted nucleation sites and improving crystal quality by precise positioning of the laser beam during growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional annealing methods (thermal treatment under Cd-pressure or Te-pressure) are used to eliminate Te inclusions, then Te precipitates are reduced, but electrical resistivity decreases and dislocation density increases
Solution Approach 1:
The patent applies localized laser annealing specifically at the crystal-melt interface where Te inclusions form, rather than subjecting the entire crystal to conventional annealing. This localized approach eliminates Te precipitates at their formation site without affecting the bulk crystal's electrical properties, thus maintaining high resistivity while improving manufacturing precision.
Solution Approach 2:
The patent replaces conventional thermal annealing processes with laser-induced thermo-migration. Instead of using extended thermal treatment under controlled atmospheres, a focused laser beam creates localized heating that drives Te inclusions to migrate and be eliminated through the liquid melt phase, achieving the same result with different physical mechanisms and better preserving electrical resistivity.
2Manufacturing precision
If high temperature annealing (500-900°C) is applied to reduce Te precipitates, then Te inclusions are eliminated, but substrate quality deteriorates due to increased dislocation density
Solution Approach 1:
The patent employs pulsed laser heating rather than continuous high-temperature annealing. The periodic pulsed action delivers energy in controlled bursts that are sufficient to melt and remove Te inclusions through thermo-migration, while the intermittent nature of the heating prevents the excessive thermal stress and dislocation formation associated with prolonged high-temperature treatment.
Solution Approach 2:
The patent substitutes conventional high-temperature thermal annealing with laser-induced localized melting and thermo-migration. This replacement allows Te inclusion elimination through a different mechanism that operates at lower effective temperatures and shorter durations, thereby preserving substrate quality while achieving the same manufacturing precision improvement.
3Manufacturing precision
If conventional thermal annealing is used to eliminate Te inclusions, then Te precipitates are removed, but the process is time-consuming and complex
Solution Approach 1:
The patent replaces lengthy conventional annealing processes with rapid laser-induced thermo-migration. The focused laser beam creates localized melting and drives Te inclusion removal through the liquid phase in a matter of seconds to minutes, compared to hours for conventional thermal treatment, thus eliminating time loss while maintaining manufacturing precision.
Solution Approach 2:
The use of pulsed laser heating enables rapid, intermittent energy delivery that achieves Te inclusion elimination much faster than continuous thermal annealing. The periodic action allows the system to reach the necessary thermal state quickly and maintain it only long enough to remove inclusions, significantly reducing the total process time while preserving manufacturing precision.
4Use of energy by moving object
If laser annealing at 10.2 μm wavelength is used, then the sample is transparent and heating is uniform, but Te inclusion absorption is low resulting in slow thermo-migration (3 μm/h at most)
Solution Approach 1:
The patent changes the laser wavelength parameter from 10.2 μm to 1.064 μm (fundamental wavelength of Nd:YAG laser). This parameter change exploits the strong absorption band of tellurium at 1.064 μm, increasing energy absorption by Te inclusions from weak to strong, which directly accelerates the thermo-migration speed from 3 μm/h to effective elimination rates, while maintaining the transparency and uniform heating benefits.
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
This approach effectively removes Te precipitates and inclusions, enhancing crystal quality and growth yield by healing defects and reducing multiple grain formation, while avoiding high-temperature processes that alter the defect equilibrium.
Implementation Method 1
A laser mounted on to the furnace and by radiating a beam across the growing crystal at or near the interface between the grown crystal portion and a melt portion of the crystal material will help melting any Te precipitates or inclusions formed in the crystal during growth
Implementation Method 2
The Te precipitates and inclusions are locally heated at the crystal-melt interface or close to crystal-melt interface to induce thermo-migration of Te impurities
Implementation Method 3
The mechanism is driven by the strong absorption of the light by tellurium inclusions. The amount of energy transferred to the system is compatible with the proposed thermo-diffusion mechanism
Implementation Method 4
calculations however showed that by using laser pulses of longer duration (100 ns) it is possible to melt and make diffuse also large tellurium inclusions without damaging the sample surface
Data Source
AI summary
In a crystal growth furnace having an array of vertically arranged heaters to provide controlled heating zones within a chamber, and a crucible for holding crystal material, wherein the crystal is grown vertically through the heating zones, the improvement includes a laser mounted outside the chamber which radiates a beam of energy to locally melt precipitates and inclusions. The furnace includes a mechanism to position the laser vertically to, at or near the interface between the formed crystal and crystal melt material above the formed crystal. The crystal material can be CdZnTe.