Ultrabroadband　photodetectors　(PDs)　working　in　the　frequency　range　from　the　UV　to　THz　regions　of　the　spectrum　play　a　crucial　role　in　integrated　multifunction　photoelectric　detection.　Even　so,　a　shortage　of　high-performance　PDs　has　seriously　restricted　the　overall　development　of　this　field.　The　present　work　demonstrates　a　high-performance,　ultrabroadband　PD　with　a　composite　nanostructure　comprising　a　suspended　carbon　nanotube　(CNT)　film　on　which　titanium　and　palladium　are　deposited.　The　application　of　titanium　and　palladium　to　the　CNT　film　in　this　device　provides　n-doping　and　p-doping,　respectively,　and　the　deposited　metal　nanoparticles　also　ensure　enhanced　thermal　localization.　This　device　exhibits　short　response　time,　high　responsivity,　large　linear　dynamic　range,　and　small　noise　equivalent　power　over　the　ultrabroadband　spectrum　based　on　a　strong　photothermoelectric　effect.　Numerical　simulation　results　also　confirm　the　effective　doping　and　enhanced　thermal　localization　in　this　PD　resulting　from　the　deposited　metals.　A　theoretical　analysis　shows　that　the　thermal　conductivity　of　the　composite　film　is　no　longer　independent　of　the　temperature　over　a　wide　temperature　range.　This　work　provides　a　simple　but　novel　strategy　for　the　design　of　high-performance　ultrabroadband　PDs.