Method for measuring the trap density in a 2-dimensional semiconductor material

Patent metadata

Field	Value
Publication number	US-11898958-B2
Application number	US-202117323115-A
Country	US
Kind code	B2
Filing date	May 18, 2021
Priority date	May 18, 2020
Publication date	Feb 13, 2024
Grant date	Feb 13, 2024

Abstract

A spot on a layer of a 2D semiconductor material deposited on a substrate is irradiated so as to generate excitons, so that photons are emitted from the layer. The photoluminescence spectrum is recorded for different values of the charge carrier concentration in the layer. The modulation of the charge carrier concentration may be realized by modulating the output power of the light source used to irradiate the sample. The relation is recorded between the ratio of the photoluminescence intensity of a first peak in the spectrum related to radiative recombination from indirect bandgaps to the intensity of a second peak in the spectrum related to radiative recombination from direct bandgaps, and the carrier concentration. This relation is fitted to a model of the ratio that takes into account multiple recombination mechanisms, radiative and non-radiative. From this process, the trap density within the bandgap is derived.

First claim

What is claimed is:

1. A method comprising:
illuminating a layer of a two-dimensional (2D) semiconductor material with a first light beam having a first intensity, thereby generating first electron-hole pairs having a first concentration;
determining a first direct photoluminescence intensity Idir corresponding to direct bandgap radiative combination of the first electron-hole pairs and a first indirect photoluminescence intensity I ind corresponding to indirect bandgap radiative combination of the first electron-hole pairs;
illuminating the layer with a second light beam having a second intensity that is different from the first intensity, thereby generating second electron-hole pairs having a second concentration that is different from the first concentration;
determining a second direct photoluminescence intensity Ian corresponding to direct bandgap radiative combination of the second electron-hole pairs and a second indirect photoluminescence intensity L ind corresponding to indirect bandgap radiative combination of the second electron-hole pairs; and
determining a trap density of the layer based on the first concentration, the second concentration, the first direct photoluminescence intensity, the first indirect photoluminescence intensity, the second direct photoluminescence intensity, and the second indirect photoluminescence intensity.

2. The method according to claim 1 , wherein the layer of the 2D semiconductor material is deposited on a dielectric layer that is deposited on an electrically conductive substrate, the method further comprising:
applying a first voltage between the layer of the 2D semiconductor material and the electrically conductive substrate while illuminating the layer of the 2D semiconductor material with the first light beam; and
applying a second voltage between the layer of the 2D semiconductor material and the electrically conductive substrate while illuminating the layer of the 2D semiconductor material with the second light beam, wherein the second voltage is different from the first voltage.

3. The method according to claim 1 , wherein the layer of the 2D semiconductor material comprises at least two monolayers of a transition metal dichalcogenide (TMDC).

4. The method according to claim 3 , wherein the TMDC is MoS 2 or WS 2 .

5. The method according to claim 1 , wherein determining the trap density comprises determining the trap density using:

I
ind

I
dir

∝

1

τ

r
⁢
ad

-
ind

e
⁢
f
⁢
f

⁢
B
⁢

n
d

⁢

N
2

(

1
-

F
d

)

+
1
+
a

+
b

wherein τ rad−ind eff is a radiative lifetime of electron-hole pairs in the indirect bandgap, B is the Auger rate constant, N is the carrier concentration, n d the trap density, F d the defect occupancy state, and a and b are correction terms which account for experimental uncertainties.

6. The method according to claim 1 , wherein determining the trap density comprises confirming the trap density during in-line processing of the 2D semiconductor material.

7. The method according to claim 1 , wherein determining the trap density comprises determining the trap density based on a ratio of the first indirect photoluminescence intensity to the first direct photoluminescence intensity.

8. The method according to claim 1 , wherein determining the trap density comprises determining the trap density based on a ratio of the second indirect photoluminescence intensity to the second direct photoluminescence intensity.

9. The method according to claim 1 , wherein the first light beam or the second light beam comprises a laser.

Assignees

• Imec Vzw
• Univ Leuven Kath
• Katholieke Univ

Inventors

• Leonhardt Alessandra
• Lockhart De La Rosa Cesar Javier
• De Gendt Stefan
• Huyghebaert Cedric
• Brems Steven
• Nuytten Thomas

Classifications

• G01N21/6489 Primary

  Photoluminescence of semiconductors · CPC title

• G01N21/9501

  Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20) · CPC title

• G01N21/6408

  with measurement of decay time, time resolved fluorescence · CPC title

• G01N2021/646

  Detecting fluorescent inhomogeneities at a position, e.g. for detecting defects · CPC title