Method of optimizing the EMI shielding and infrared transparency of GaAs IR windows

Patent metadata

Field	Value
Publication number	US-12203192-B2
Application number	US-202218072931-A
Country	US
Kind code	B2
Filing date	Dec 1, 2022
Priority date	Dec 1, 2022
Publication date	Jan 21, 2025
Grant date	Jan 21, 2025

Abstract

A method of manufacturing a structurally competent, EMI-shielded IR window includes using a mathematical model that combines the Sotoodeh and Nag models to determine an optimal thickness and dopant concentration of a doped layer of GaAs or GaP. A slab of GaAs or GaP is prepared, and a doped layer of the same material having the optimal thickness and dopant concentration is applied thereto. In embodiments, the doped layer is applied by an HVPE method such as LP-HVPE, which can also provide enhanced GaAs transparency near 1 micron. The Drude model can be applied to assist in selecting an anti-reflective coating. If the model predicts that the requirements of an application cannot be met by a doped layer alone, a doped layer can be applied that exceeds the required IR transparency, and a metallic grid can be applied to improve the EMI shielding, thereby satisfying the requirements.

First claim

We claim:

1. A method of designing and manufacturing an EMI shielded infrared (IR) window suitable for a specified application having specified size, transparency, and EMI shielding requirements, the method comprising:
preparing a slab of GaAs or GaP according to the size requirement of the specified application, the slab having sufficient thickness to meet a structural competence requirement of the specified application;
selecting a plurality of candidate parameter combinations comprising combinations of candidate dopant concentrations and candidate layer thicknesses for a doped conductive layer to be applied to the slab, the doped layer being a doped layer of GaAs if the slab is a GaAs slab, the doped layer being a doped layer of GaP if the slab is a GaP slab;
applying a model to the candidate parameter combinations, thereby for each of the candidate parameter combinations estimating an IR absorption and a sheet conductivity of the doped conductive layer, wherein applying the model comprises:
applying an empirical low field mobility model according to Sotoodeh, thereby estimating a carrier mobility of the doped conductive layer;
calculating an estimated sheet resistance of the doped conductive layer according to the candidate parameters and the estimated carrier mobility; and
applying a quantum mechanical defect scattering model of free carrier absorption based upon a relationship taught by Nag, thereby estimating the IR absorption of the doped conductive layer according to the candidate layer thickness and the estimated sheet resistance of the doped conductive layer;

repeating the steps of selecting candidate parameters and applying the model thereto until an optimal combination of layer thickness and dopant concentration are determined; and
if the model predicts that applying the doped semiconductor layer having the determined optimal combination of layer thickness and dopant concentration will meet the transparency and EMI shielding requirements of the specified application, applying the doped conductive layer to the slab according to the determined optimal combination of layer thickness and dopant concentration.

2. The method of claim 1 , wherein the doped conductive layer is applied to the slab by a vacuum deposition process.

3. The method of claim 1 , wherein the doped conductive layer is applied to the slab by hydride vapor phase epitaxy (HVPE).

4. The method of claim 3 , wherein the doped conductive layer is applied to the slab by low pressure HVPE (LP-HVPE).

5. The method of claim 1 , further comprising applying an anti-reflective (AR) coating onto the doped conductive layer.

6. The method of claim 5 , wherein the method further comprises:
applying a Drude model to estimate a real part of an index of refraction of the doped conductive layer; and
selecting the AR coating at least in part according to the estimated real part of the index of refraction of the doped conductive layer.

7. The method of claim 1 , wherein the slab is a GaAs slab, and preparing the slab includes growing the GaAs slab using HPVE.

8. The method of claim 7 , wherein preparing the slab includes growing the GaAs slab using LP-HPVE.

9. The method of claim 7 , wherein the doped conductive layer is applied to the slab as part of the HVPE process that is used to grow the slab.

10. The method of claim 1 , wherein the method further comprises, if the model predicts that applying the doped semiconductor layer having the determined optimal combination of layer thickness and dopant concentration will not meet the transparency and EMI shielding requirements of the specified application:
applying the doped conductive layer to the slab with a combination of layer thickness and dopant concentration that exceeds the transparency requirement of the application; and
applying a metallic grid to the slab having a thickness and grid spacing sufficient to cause the combined metallic grid and doped semiconductor EMI shielding to meet both of the transparency and EMI shielding requirements of the specified application.

Assignees

• Bae Sys Inf & Elect Sys Integ

Inventors

• Reeves Jeremy B
• Zawilski Kevin T
• Schunemann Peter G

Classifications

• H05K9/0094

  being light-transmitting, e.g. transparent, translucent · CPC title

• C30B29/42

  Gallium arsenide · CPC title

• C30B25/16

  Controlling or regulating (controlling or regulating in general G05) · CPC title

• C09D5/006 Primary

  Anti-reflective coatings · CPC title

• H05K9/0005

  Shielded windows · CPC title