News & Analysis
/
Article

Creating gallium arsenide photocathodes with high quantum efficiencies

FEB 12, 2021
Method for activating GaAs photocathodes using an initial surface heat-cleaning step.
Creating gallium arsenide photocathodes with high quantum efficiencies internal name

Creating gallium arsenide photocathodes with high quantum efficiencies lead image

Biswas et al. report a method for creating activated gallium arsenide (GaAs) photocathodes with both improved lifetimes and high quantum efficiencies (QE). The activation process used cesium (Cs), tellurium (Te), and molecular oxygen (O2).

This advance has implications for high energy physics and advanced electron microscopy. GaAs photocathodes are an important component of future electron accelerators that rely on polarized beams.

To extend the lifetime of GaAs photocathodes, previous investigators developed methods to activate the surface with low electron affinity materials, such as Cs2Te. While this improves the lifetime, the resulting material often has a low QE.

The scientists addressed this by heat cleaning the surface at an optimal temperature, then depositing cesium and tellurium in alternating cycles. The maximum QE observed in this first study was 6.6% at 532 nm laser illumination.

“Although this is the highest QE reported so far for Cs-Te activated GaAs photocathodes, it is still not as high as the QE of typical Cs-O activated GaAs photocathodes, typically about 10%,” said author Jyoti Biswas.

To increase the QE, the scientists activated a second heat-cleaned surface by codepositing cesium and oxygen, followed by alternating deposition cycles with tellurium. A 532 nm laser diode was used to follow changes in QE during this process. The maximum QE obtained by this second attempt was 8.8% at 532 nm laser illumination.

Photoemission of polarized electrons requires a negative electron affinity. To achieve this, the work function in a doped semiconductor should be lower than the semiconductor’s bandgap.

“In the Cs-O-Te activation process, both the GaAs-Cs and Cs-O dipoles contribute to the work function reduction,” said author Erdong Wang. This brings the work function below the bandgap value.

Source: “High quantum efficiency GaAs photocathodes activated with Cs, O2, and Te,” by Jyoti Biswas, Erdong Wang, Mengjia Gaowei, Wei Liu, Omer Rahman, and Jerzy T. Sadowski, AIP Advances (2021) The article can be accessed at https://doi.org/10.1063/5.0026839 .

Related Topics
More Science
/
Article
Pentagonal-shaped photonic-crystal lightsails could one day propel tiny spacecraft to other stars.
APS
/
Article
A new study of complex systems supports a growing trend that focuses more on analyzing a system’s collective behavior rather than on trying to uncover the underlying interaction mechanisms.
AAS
/
Article
An team of astronomers has obtained high-resolution images of all known protoplanetary disks in the Lupus star-forming region
AAS
/
Article
Could there have been two massive black holes in our galaxy’s center at one time? New modeling of fast-moving stars in the Milky Way’s halo suggests the answer is yes.