Text this: Impact of Temperature and Doping on the Performance of <inline-formula><tex-math notation="LaTeX">${{\bf Ge}}/{{\bf G}}{{{\bf e}}_{1 - {\boldsymbol{x}}}}{{\bf S}}{{{\bf n}}_{\boldsymbol{x}}}/{{\bf Ge}}$</tex-math></inline-formula> Heterojunction Phototransistors