Carbon-doped long wavelength GaAs/AlxGa1−xAs quantum well infrared photodetectors grown by organometallic vapor phase epitaxy

We report p‐doped long wavelength GaAs/Al_xGa_1−xAs quantum well infrared photodetectors (QWIP) grown by organometallic vapor phase epitaxy. The operation of these devices is based on the photocurrent induced through valence‐band intersubband absorption by holes and, unlike n‐doped QWIPs, can utilize normal incidence illumination. Carbon was used as the p‐type dopant in a low‐pressure (30 Torr) vertical‐geometry reactor. The C‐doped QWIPs consisted of fifty periods of 54‐nm‐thick undoped Al_xGa_1−xAs (x=0.36 or 0.30) and C‐doped GaAs wells (L_z=4 or 5 nm). Using normal incidence illumination, the C‐doped QWIP with shorter wavelength response (x=0.36, L_z=4 nm) exhibited a quantum efficiency of η=21.4% and a detectivity at the peak wavelength of D_λ=5.4×10⁹ cm √Hz/W at 77 K. The peak and cutoff wavelengths were λ_p=8.1 μm and λ_co=8.9 μm, respectively. The C‐doped QWIP with longer wavelength response (x=0.30, L_z=5 nm) exhibited a normal incidence η=22.1% and $D_{\lambda }^{*}$ =3.5×10⁸ cm √Hz/W for λ_p=10.5 μm (λ_co=11.7 μm). The detectivity of the C‐doped QWIPs is about four times less than n‐doped QWIPs for the same λ_p but have the advantage of utilizing normal incidence illumination.