Graphene is considered a suitable atomically thick layer on photocathodes, and the photoemission performance of the graphene-covered photocathodes can be enhanced through Cs/O activation. To investigate the effects of the substrate materials beneath the graphene layer on Cs/O deposition and photoemission performance. We compare the activation processes and photoemission performances of few-layer graphene supported by nickel and copper to investigate the effects of the substrate materials beneath the graphene layer on Cs/O deposition and photoemission performance. By Cs/O activation, the nickel-supported few-layer graphene can possess a higher response at 405 nm, while the copper-supported cathode can acquire a wider spectral response and better stability. After degradation, we discover that the samples supported by nickel and copper can act differently through the additional Cs/O deposition processes, while the surface barrier heights of both samples are further decreased.
To research the attenuation performance of the AlGaN photocathode, three samples with same structures grown by metalorganic chemical vapor deposition (MOCVD) were activated with three different activation methods, which are Cs-only, Cs-O and Cs-O-Cs activation, respectively. The spectral responses and attenuated photocurrents of three AlGaN photocathodes were measured, the result shows that the Cs-O activated AlGaN photocathode have the lowest attenuation speed in the first few hours, the next are Cs-O-Cs and Cs-only activation, respectively. After the Cs-O-Cs activation sample has attenuated 90 min, its attenuation photocurrent curve is coincident with the Cs-O activation sample in the next measurement. The main factor which affects the photocurrent attenuation is Cs atom desorbed from the photocathodes surface.
AlxGa1-xN photocathode was prepared by MOCVD and the reflectivity, transmittance, and absorptivity were test. Based on thin film principle, optical model of t-mode AlxGa1-xN photocathodes was built, and then optical properties and quantum efficiencies were simulated. Results show that AlxGa1-xN photocathodes satisfy the need of detectors with “solar blind” property when the Al component is larger than 0.250. There is an optimal thickness of AlxGa1-xN layer to obtain highest quantum efficiency, and the optimal thickness is 0.3μm. There is close relation between absorptivity and quantum efficiency, which is in good agreement with the “three-step” model. This work gives a reference for the design and preparation of AlxGa1-xN photocathodes.
The AlGaN/GaN with thin GaN surface was grown by metalorganic chemical vapor deposition (MOCVD). And one of
two AlGaN/GaN photocathode samples was etched by molten KOH about 40s, and its reflectivity and transmittance are
tested. The thickness of AlGaN and GaN layers are fitted by the matrix formula for thin film optics, and the GaN
thickness of them are 7nm and 2.5nm respectively. And etch speed of GaN are got in molten KOH at about 400°C. Then
the etched and original AlGaN/GaN photocathode samples are activated by Cs/O in the same way. The spectral response
and the result of simulation show that the cut-off wavelength of the etched AlGaN/GaN deviate to the short-wave. And
the quantum efficiency decline with the GaN thickness decrease.
In order to obtain the suitable photocathode which could be applicable for the field of ocean exploration, the p-type zinc (Zn)-doped reflection-mode GaAlAs photocathode sample using exponential-doping technique is grown by metal organic chemical vapor deposition, the Al component of GaAlAs emission layer is designed to be 0.63. After the chemical etching, the photocathode samples are heated in vacuum at high-temperature of 650°C and 600°C respectively, the vacuum variation curves during the heat cleaning are measured, which correspond to the desorption of oxides in the surface of GaAlAs emission layer. The (Cs, O) activation for the photocathodes is executed after heat cleaning. Different proportion of Cs and O is performed on the different photocathode samples. The activation photocurrent curves of two samples with different heat cleaning temperature show that the GaAlAs surface treated by higher heat cleaning temperature is more sensitive to the Cs-O adsorption. The photocathode activated with the larger Cs current has a shorter time to reach the first photocurrent peak, and also obtains a bigger final photocurrent peak. According to the measured spectral response curves, it could be found that a suitable heat cleaning temperature and a moderate Cs/O current ratio are very important to prepare high performance GaAlAs photocathode. The prepared reflection-mode GaAlAs photocathodes are response to the blue-green light, and the cut-off wavelength is at about 580 nm.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.