Gallium Arsenide (GaAs) Solar Cells

Gallium Arsenide (GaAs) is a compound of two basic elements; Gallium and Arsenic. It is III-V direct bandgap semiconductor with 1.41 eV band gap, so relatively it can absorb (AM 1.5G spectrum) light more efficiently. This band gap can be varied by Aluminium (Al) or Indium (In) like AlGaAs or InGaAs. First GaAs solar cell was used in space application for Venera 3 mission and then till now, its efficiency has reached up to 29.1 % by Alta Devices. To check the efficiency of all types of solar cells, click here.

                      GaAs has several advantages over Silicon such as higher temperature applications and higher carrier mobility. But is 5 to 10 times expensive than silicon and due to direct bandgap radiative recombination is also dominating.

Gallium Arsenide (GaAs) unit cell representation

In other semiconducting materials that are being used in solar applications, efficiency reduces with increase in temperature. But GaAs has a low-temperature coefficient, thus it is not much affected by increasing temperature. In GaAs elements used for N-type doping are Selenium (Se), Silicon (Si) and Tin (Sn) while elements used for P-type doping are Zinc (Zn), Magnesium (Mg) and Carbon (C). With lower resistance and higher carrier mobility, GaAs creates less noise in electronic circuits at high frequencies. Although being expensive GaAs finds it's applications in other technologies like satellites, military applications and ICs.

Note

Mobility
Mobility is defined as how quickly the charge carrier can move within the semiconductor. In GaAs electron mobility (μ_e) and hole mobility (μ_h) is in the range of
(μ_e) = 5000 to 10000 V/cm²
(μ_h) = 100 to 400 V/cm²

Carrier Life Time
It is the average time taken by the minority carrier in the excited state to recombine. In GaAs electron lifetime (T_e) and hole lifetime (T_h) is in the range of
(T_e) = 1 microsecond to few nanoseconds
(T_h) = few nanoseconds.

For solar applications, GaAs solar cell provides high mobility and high carrier lifetime which cause lower recombination possibilities and higher efficiency is obtained.