Trouble understanding charge transfer in photodetectors

[edimz]

TL;DR Summary

Trouble understanding charge transfer in photodetectors

Hi,

I have some trouble understanding the charge transfer process in photodetectors that are built from two different semiconductors, creating depletion region.

To my knowledge, to make an effective detector, there needs to be effective charge separation, in order to avoid recombination. However, looking at different articles it’s seems like Heterostructures type 1 (in which both electrons and holes expected to migrate to one of the materials) is the most suitable for detectors, but It doesn’t make sense to me if the goal is to separate the charges.. I would have thought that type 2 would be more suitable choice.

May someone explain what went wrong with my intuition?

Thanks!

 

[phyzguy]

Maybe before worrying about heterojunctions, you should make sure you are familiar with a simple PN junction. I recommend reading about PN junctions and how the depletion region forms between the P-type region and the N-type region. Once you have that down, ask yourself what happens if a photon comes in and creates a hole-electron pair in the middle of the depletion region. Once you have that down (maybe you already do), we can talk about heterojunctions. For this, please give us a reference to what you are reading about type 1 and type 2 heterojunctions, preferably with some diagrams.

 

[Astronuc]

TL;DR Summary: Trouble understanding charge transfer in photodetectors

To my knowledge, to make an effective detector, there needs to be effective charge separation, in order to avoid recombination. However, looking at different articles it’s seems like Heterostructures type 1 (in which both electrons and holes expected to migrate to one of the materials) is the most suitable for detectors, but It doesn’t make sense to me if the goal is to separate the charges.. I would have thought that type 2 would be more suitable choice.

As phyzguy indicated, it would help to know what references one is reading. What type(s) of semiconductors: 1) metal, 2) metal oxide, 3) metal dichalcogenides (TMDs), . . . ?
Charge separation/recombination is one of several factors.
I happened to come across an article: Enhancing the Photoelectric Performance of Photodetectors Based on Metal Oxide Semiconductors by Charge-Carrier Engineering, which makes the following points:

In general, the photoelectric conversion processes from optical signals to electric signals via semiconductor-based PDs mainly involve four steps:

1) Generation of the Charge Carriers: When the incident photons are absorbed by the semiconductors after the light trapping process, the photo-excited electrons transit from the valence band (VB) to the conduction band (CB) of the semiconductors, while the corresponding holes are left in the VB. The obtained electrons in the CB and holes in the VB are recognized as the photo-induced carriers.

2) Separation of the Charge Carriers: Forced by the applied electric field or built-in electric field formed at the interface of heterojunctions, the photo-induced electron–hole pairs are separated and move toward different electrodes.

3) Transportation of the Charge Carriers: After being separated, the different charge carriers would travel along the conduction pathways toward alternative electrodes, where the tapping [sic, trapping?] and recombination of charges carrier occur and cause decreased photoelectric conversion efficiency.

4) Extraction of the charge Carriers: After the charge carriers arrived at the electrodes, in accordance with the varied electrode configurations, they will be extracted and conducted to the external circuit, which contribute to the photocurrent

Ref: https://fxs.fudan.edu.cn/paper/downloads/2019_6.pdf

An example of Type III heterostructures
High-performance photodetectors based on band alignment of type-I Te/WSe₂ and type-III Te/ReS₂ van der Waals heterostructures
https://www.sciencedirect.com/science/article/abs/pii/S0009261423005547?via=ihub

Metal oxide and other semiconductor interactions with photons have broad application to corrosion and radiation detection, as well as optoelectronics.