Influence of metal–semiconductor interface treatments and absorber structure on the performance and reliability of uni-traveling-carrier photodiodes (UTC-PDs)

The effects of absorber structure-controlled by adjusting the thickness ratio of doped and undoped InGaAs layers-and metal-semiconductor interface treatment methods were investigated in waveguide-type UTC-PDs. Ultraviolet-ozone (UVO) and ammonia solution cleaning of the InGaAs surface improved the interface quality in terms of contact resistivity and bias-temperature stability. Nevertheless, devices cleaned using buffered oxide etchant (BOE) exhibited higher photoresponsivity and superior frequency characteristics. This phenomenon is attributed to the reduction of dark current (I_Dark) caused by the residual interfacial oxide layer at the metal/InGaAs interface. In contrast, the influence of absorber structure variation was negligible. These results demonstrate that the interface condition plays a more dominant role than absorber modification in determining device performance. Therefore, optimizing the interface condition while maintaining a high-quality oxide layer is essential for further enhancing UTC-PD performance.