22.2 Photoconductors
595
(a)
(b)
Fig. 22.7 a AlGaAs/GaAs QWIP absorption spectrum for multiple reflection geometry. Adapted from [1829]. b Transmission of AlGaAs/GaAs QWIP (100 QWs) in double reflection geometry (45 ◦ angle of incidence). The well doping is
1.0 × 10 12 cm −2 (dashed line) and 1.5 × 10 12 cm −2 (solid line). Adapted from [1830]
(a)
0 10 20 30 40 50 60 70 80 90
(b)
0 10 20 30 40 50 60 70 80 90
Fig. 22.8 Dependence of the QWIP response on a polarization and b angle of incidence. Dashed lines are guides to the
eye. Adapted from [1829]
quantum dots (lateral confinement). Also, a grating can be used to create a finite angle of incidence
(Fig. 22.9b).
Besides a useful detectivity (2 × 10
10 cm Hz
1/2 /W at 77 K) QWIPs have the advantage, e.g. against
HgCdTe interband absorbers, that the highly developed GaAs planar technology is available for the
fabrication of focal plane arrays (FPA) as shown in Fig. 22.10. A FPA is an image sensor (in the focal
plane of an imaging infrared optics) and is used, e.g., for the detection of heat leaks in buildings or
night surveillance. In particular, night vision support in cars may become a major market. A competing
technology are bolometric arrays with thermally insulated pixels based on MEMS technology. A review
of FPA technologies can be found in [1831].
The carriers that have been optically excited into the upper state leave the QW by tunneling or
thermionic emission. Also, a QWIP can be made based on the direct transfer from the (populated)
subband into the continuum.
The incoming infrared radiation creates a photocurrent density of
i ph = e η w ,
(22.14)
595
(a)
(b)
Fig. 22.7 a AlGaAs/GaAs QWIP absorption spectrum for multiple reflection geometry. Adapted from [1829]. b Transmission of AlGaAs/GaAs QWIP (100 QWs) in double reflection geometry (45 ◦ angle of incidence). The well doping is
1.0 × 10 12 cm −2 (dashed line) and 1.5 × 10 12 cm −2 (solid line). Adapted from [1830]
(a)
0 10 20 30 40 50 60 70 80 90
(b)
0 10 20 30 40 50 60 70 80 90
Fig. 22.8 Dependence of the QWIP response on a polarization and b angle of incidence. Dashed lines are guides to the
eye. Adapted from [1829]
quantum dots (lateral confinement). Also, a grating can be used to create a finite angle of incidence
(Fig. 22.9b).
Besides a useful detectivity (2 × 10
10 cm Hz
1/2 /W at 77 K) QWIPs have the advantage, e.g. against
HgCdTe interband absorbers, that the highly developed GaAs planar technology is available for the
fabrication of focal plane arrays (FPA) as shown in Fig. 22.10. A FPA is an image sensor (in the focal
plane of an imaging infrared optics) and is used, e.g., for the detection of heat leaks in buildings or
night surveillance. In particular, night vision support in cars may become a major market. A competing
technology are bolometric arrays with thermally insulated pixels based on MEMS technology. A review
of FPA technologies can be found in [1831].
The carriers that have been optically excited into the upper state leave the QW by tunneling or
thermionic emission. Also, a QWIP can be made based on the direct transfer from the (populated)
subband into the continuum.
The incoming infrared radiation creates a photocurrent density of
i ph = e η w ,
(22.14)