Process for the post-deposition treament of colloidal quantum dot photodetector films to improve performance by using hydrogen peroxide

Abstract

A process for the post-deposition treatment of colloidal quantum dot films to improve photodetector performance. A colloidal quantum dot film is first deposited on a suitable substrate or device structure, given a ligand exchange, and then allowed to dry into a completed film. Next, a solution is prepared consisting of dilute H.sub.2O.sub.2 mixed with a polar solvent such as isopropyl alcohol solution. The prepared film and substrate are then immersed into the prepared solution over a set interval of time. After which, the film is removed and rinsed with solvent, then dried with clean N.sub.2 gas. After this treatment, the colloidal quantum dot film is ready for use as a photodetector.

Claims

1. A method of treating a workpiece, comprising the steps of: providing a workpiece comprising a colloidal quantum dot (CQD) film deposited on a substrate, the substrate comprising a device structure, an electronic circuit, a host material or other dot film, the CQD film deposited leaving a film surface exposed to chemical treatments; providing a first volume of diluted H.sub.2O.sub.2; adding de-ionized water to provide a second volume; adding the second volume to isopropyl alcohol forming a treatment solution; immersing the workpiece into the treatment solution; and removing the workpiece from the treatment solution.

2. The method according to claim 1, comprising the further steps of: after the step of removing the workpiece, rinsing the workpiece with polar or non-polar solvent; and flowing inert N.sub.2 gas over the CQD film.

3. The method according to claim 2, further defined by the step of: preparation of a container which will house the treatment reaction, capture excess treatment solution and chemical waste from the process, but with sufficient volume to contain the film, substrate, and treatment solution; wherein the step of immersing the workpiece into the treatment solution is further defined in that the CQD film and substrate are immersed for a given duration suitable to the photodetector film not to be less than 5 seconds; wherein the step of rinsing the workpiece with polar or non-polar solvent is further defined in that the CQD film is immediately rinsed with the inert polar or non-polar solvent flowing over the film and substrate; wherein the step of flowing inert N.sub.2 gas over the CQD film is further defined in that the use of flowing inert N.sub.2 gas is of sufficient purity not to introduce new contaminants and which is used to remove any lingering treatment solution or rinsing isopropyl alcohol.

4. A method of a post-deposition treatment of a colloidal quantum dot (CQD) film, comprising the steps of: providing a workpiece comprised of a CQD film deposited on a substrate; preparing a treatment solution by providing a first volume of X mL of 30% dilute by volume H.sub.2O.sub.2; adding the first volume to 9X mL of de-ionized water to provide a second volume of 10X mL; adding the second volume to 10X mL of isopropyl alcohol forming a 20X mL treatment solution 1.5% by volume H.sub.2O.sub.2; wherein X is a number value; immersing the workpiece into the treatment solution; removing the workpiece from the treatment solution; and rinsing the workpiece with excess isopropyl alcohol.

5. The method according to claim 4, wherein X equals about 0.5.

6. The method according to claim 4, wherein the step of immersing the workpiece into the treatment solution is further defined in that the workpiece is immersed in the treatment solution for about 60 seconds.

7. The method according to claim 4, comprising a further step of, after the workpiece is rinsed with isopropyl alcohol, blowing N.sub.2 gas over the workpiece, until no treatment solution or isopropyl alcohol remains on the film.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart of an exemplary method of the present invention.

DETAILED DESCRIPTION

(2) The exemplary method of the invention should maintain the energy states of the quantum dots by reducing any surviving contaminants, or from ligands which may couple with the energy states within the confined quantum dots, leading to an increase in photodetection performance. Colloidal quantum dot film performance can be increased due to reduction in carrier loss due to contaminants and undesirable energy states provided which would otherwise interact with those states of the quantum dots. Controlled concentrations of oxidizing and reducing agents such as hydrogen peroxide should react with, consume, and eventually remove contaminants, or even replace the organic binding ligands in the film. These agents, when used under the exemplary concentrations and times set forth herein should not damage the CQD nano-crystal structures, nor remove desirable extrinsic atomic species or ligands, nor cause the nano-crystals to agglomerate into grains, nor remove their quantum confinement.

(3) While various embodiments of the present invention have been described, it should be understood that other modifications and alternatives can be made without departing from the spirit and scope of the invention which should be determined from the appended claims. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred.

(4) While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit this invention to the specific embodiments illustrated.

(5) This invented process provides for a post-deposition treatment of a CQD film which can improve its electrical and optical performance. This process will follow the flowchart in FIG. 1, and each section marked with the corresponding number.

(6) Initially, the CQD film to be treated is first deposited on a substrate in step 100 in any of a variety of ways using common present-day techniques, or new techniques yet unforeseen. The treatment solution may be tailored to the targeted material system to be improved, as well as altered to adjust for variations in thickness, surface uniformity, H.sub.2O.sub.2 concentration, suspected contaminants arising from the CQD solutions preparation or deposition, or other factors.

(7) Next, in step 104 a ligand exchange is performed on the CQD film.

Example 1

(8) After step 104, a post-deposition treatment process and treatment solution preparation for a deposited CQD film is performed as described below. It is preferred that listed steps be performed in an ISO Class 10/100 or superior clean room environment with suitably trained personnel.

(9) In this embodiment and method of the invention, the CQD film can be comprised of HgTe quantum dots with an average diameter of 12 nm and has been deposited 3 μm thick through a drop-casting method on a silicon wafer with two electrical traces which can provide an electrical bias to the CQD film.

(10) Preparation of the Treatment Solution

(11) Given this material system, thickness, and expected surface uniformity, the solution will be prepared as follows. Listed volumes may be scaled up proportionally if a larger volume of solution is required.

(12) In step 108, 0.5 mL of 30% dilute by volume H.sub.2O.sub.2 is added to 4.5 mL of de-ionized water. Next, this newly prepared 5 mL of 3.0% dilute H.sub.2O.sub.2 is added to 5 mL of isopropyl alcohol forming a 10 mL treatment solution 1.5% by volume H.sub.2O.sub.2.

(13) Thus, the exemplary embodiment treatment solution for a CQD film, is composed of: H.sub.2O.sub.2, water, and a polar or non-polar solvent, wherein by volume, the H.sub.2O.sub.2 is about 1.5%; the water is about 48.5% and the solvent is about 50%.

(14) In more general terms, the exemplary embodiment solution is prepared by providing a first volume of X mL of about 30% dilute by volume H.sub.2O.sub.2; adding the first volume to 9X mL of de-ionized water to provide a second volume of 10X mL; adding the second volume to 10X mL of isopropyl alcohol forming a 20X mL treatment solution of 1.5% by volume H.sub.2O.sub.2; wherein X is a number value, and wherein for example “9X” is X multiplied by 9.

(15) Immersion of the CQD Film in the Solution

(16) Next, in step 112, the treatment solution can be transferred to a treatment container which can accommodate the volume of the solution, the substrate and deposited CQD film. The treatment solution should be of sufficient volume to ensure that the substrate and CQD film are fully immersed in the solution for the duration of the treatment.

(17) Next, the CQD film and substrate are entirely immersed within the solution for a treatment duration. For the given material system and thickness, a 60 second duration is used.

(18) In step 116, after the treatment duration has elapsed, the CQD film and substrate are immediately removed and rinsed with excess isopropyl alcohol likely exceeding 50 mL of volume.

(19) Cleaning of the Film and Disposal

(20) After the rinse, in step 120, clean, room-temperature inert N.sub.2 gas will be blown over the film and substrate, ensuring that no treatment solution or isopropyl alcohol remains on the film. The rinsed isopropyl and remaining treatment solution may then be properly disposed of using chemical disposal procedures.