Diffraction-Grating-Free Very Small-Pitch High-x InP/In_xGa_1-x as Quantum Well Infrared Photodetectors

Grating-free high-x InP/InxGa1-xAs mid-wavelength infrared QWIP focal plane array

“…Grating-free FPA implementation of a high-x InP/InxGa1-xAs material system with GaInP barriers was also reported recently [11]. The following work [12] implemented in the authors' research laboratory on variable pitch (down to a pixel area of 49 m 2 ) grating-free MWIR InP/In0.85Ga0.15As pixel arrays demonstrated desirable performance with 70% CE and f/2 specific detectivity of 1.5•10 11 cmHz 1/2 /W at 78 K at the bias voltages applicable by commercial read-out integrated circuits (ROICs). Furthermore, the characteristics of the pixels including the dark current perfectly scaled with the pixel area exhibiting an advantage over the alternative technologies suffering from pitch reduction problems.…”

“…The peak responsivity reaches 3 A/W under a −3.5 V bias corresponding to a CE as high as 67% while maintaining an almost bias-independent f/2 specific detectivity of 1.5•10 11 cmHz 1/2 /W at 78 K together with a 22% peak quantum efficiency [12]. The sensors did not exhibit 1/f noise down to 1 Hz, and the normalized responsivity did not exhibit any considerable dependence on the bias voltage magnitude and polarity [12].…”

“…The grating-free FPA was fabricated through processes similar to those utilized for the variable pitch pixel arrays whose detailed characteristics were reported earlier [12]. The fabrication procedure included mesa etching, ohmic contact formation, passivation, under-bump metallization, In-coating and lift-off for bump formation, hybridization with a direct injection ROIC and substrate thinning to 30 µm.…”

“…Figure 1 shows the normalized spectral responsivity and the peak CE of the variable pitch pixel arrays [12], which should be identical to those of the FPA pixels due to the same epilayer structure and processing conditions used in the fabrication of the FPA and the pixel arrays. The peak responsivity reaches 3 A/W under a −3.5 V bias corresponding to a CE as high as 67% while maintaining an almost bias-independent f/2 specific detectivity of 1.5•10 11 cmHz 1/2 /W at 78 K together with a 22% peak quantum efficiency [12]. The sensors did not exhibit 1/f noise down to 1 Hz, and the normalized responsivity did not exhibit any considerable dependence on the bias voltage magnitude and polarity [12].…”

“…Furthermore, the characteristics of the pixels including the dark current perfectly scaled with the pixel area exhibiting an advantage over the alternative technologies suffering from pitch reduction problems. The molecular beam epitaxy grown epilayer structure of the InP/In0.85Ga0.15As QWIP included thirty periods of 35 Å thick In0.85Ga0.15As QW and 550 Å thick InP barrier with In0.53Ga0.47As top and bottom contacts [12]. The QWs were Si-doped to obtain a 2D electron concentration of 5•10 11 cm −2 .…”