Impact of the growth temperature on the performance of 1.70-eV Al0.22Ga0.78As solar cells grown by MBE

• Published in: Journal of crystal growth 2017-10, Vol.475, p.322-327
• Main Authors: Onno, Arthur, Tang, Mingchu, Oberbeck, Lars, Wu, Jiang, Liu, Huiyun
• Format: Article
• Language: English
• Subjects: A3. Growth temperature; A3. Molecular Beam Epitaxy; Aluminum; Arsenic; Arsenides; B2. Aluminum Gallium Arsenide; B3. Solar cells; Chemical elements; Current density; Epitaxial growth; Gallium arsenide; Impact analysis; Intermetallic compounds; Minority carriers; Molecular beam epitaxy; Open circuit voltage; Photoluminescence; Photovoltaic cells; Quantum efficiency; Solar cells; Studies; Temperature
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2017.07.011

•Five 1.70-eV Al0.22Ga0.78As solar cells were grown by MBE between 580°C and 660°C.•Performances improve when the growth temperature is increased from 580°C to 620°C.•Performances moderately decrease with a growth temperature above 620°C.•A Voc above 1.21V has been demonstrated with a growth temperature of 620°C.•A rough surface is obtained at 600°C, leading to poor optoelectronic properties. Growth of high material quality Aluminum Gallium Arsenide (AlxGa1-xAs) is known to be challenging, in particular with an Al content x above 20%. As a result, the use of AlxGa1-xAs in devices requiring high minority carrier lifetimes, such as solar cells, has been limited. Nonetheless, it has long been established that the substrate temperature is a key parameter in improving AlxGa1-xAs material quality. In order to optimize the growth temperature of 1.70-eV Al0.22Ga0.78As solar cells, five samples have been grown by Solid-Source Molecular Beam Epitaxy (SSMBE) at 580°C, 600°C, 620°C, 640°C, and 660°C, respectively. A strong improvement in performance is observed with increasing the growth temperature from 580°C to 620°C. An open-circuit voltage above 1.21V has in particular been demonstrated on the sample grown at 620°C, translating into a bandgap-voltage offset Woc below 0.5V. Above 620°C, performances – in particular the short-circuit current density – moderately decrease. This trend is confirmed by photoluminescence, current density versus voltage characterization under illumination, and external quantum efficiency measurements.