Characteristics of Germanium n+/p junctions formed by phosphorus diffusion from on indium-gallium-phosphide layer

• Characteristics of Ge n+/p junctions by achieved InGaP diffusion are investigated.
• The characteristics are estimated through a multiple error function fitting method.
• A faster diffusion occurs during the simultaneous diffusion of In/Ga/P into Ge.
• A non-annealed InGaP-deposited junction shows Ohmic behavior due to point defects.
• After 550 °C anneal, a small on/off-current ratio is obtained.

Although numerous studies have been previously reported for the formation of Ge p–n junctions, there is still a lack of research on Ge junctions formed by solid-phase diffusion doping, which typically uses the diffusion phenomenon of phosphorus (P) atoms from InGaP for the fabrication of a Ge n+/p subcell in a III–V multi-junction cell. Here, we investigate the characteristics of Ge n+/p junctions achieved by the InGaP-based diffusion technique at 450–650 °C with SIMS, ECV, and J–V analyses. In addition, through a multiple error function fitting method, diffusivity, peak position, and activation energy values are accurately estimated from raw In/Ga/P/Ge SIMS profiles. The extracted activation energy values for In/Ga/P atoms are much lower than previously reported, indicating that a faster diffusion phenomenon occurs during the simultaneous diffusion of In/Ga/P into Ge. A non-annealed InGaP-deposited junction shows Ohmic behavior with a high current density because of leakage currents by many interfacial point defects. After a 550 °C anneal, the current density is reduced by 3–4 orders of magnitude and a small on/off-current ratio is obtained. Compared to this 550 °C annealed junction, a current density increases ∼10 times in the 650 °C sample due to an increased n-type carrier concentration.