The GaAs BIB detector development program for far infrared astronomy is
continued now as a common effort of four institutions: MPE (Germany),
UC Berkeley, LBNL and NPS Monterey (USA). The actual research
program is supported by a three year NASA grant. Current experimental
work is assisted by theoretical modeling.
Rationale for a GaAs BIB (Blocked Impurity Conduction Band)
Detector Array Development:
- GaAs has the shallowest stable dopant (e.g., Te: 5.7 meV) of any
technically well-explored semiconductor.
- Extension of the photoconductive cut-off wavelength to 330
µm (30 cm-1) with GaAs BIB devices is expected, whereas the
present cut-off wavelength limit of stressed Ge:Ga photoconductors is
around 210 µm, cf. Fig. 1.
- GaAs BIB detector should get rid of g-r noise
characteristic of bulk GaAs photoconductors.
- Manufacture of planar structured two-dimensional detector arrays
at an affordable price seems feasible.
- Complexity advantage of photoconductors over bolometers and their
more demanding cooling techniques
|Fig. 1 FIR
absorption spectra of n-doped GaAs
sketch of a GaAs BIB pilot sample
- GaAs layers are grown using the Liquid Phase Epitaxy process. A
centrifuge system with magnetic bearings was set up at UCB, Fig. 3.
Growth parameters are under permanent optimization, but manufacture of
high purity blocking layers is a challenge (unwanted donor
concentration now below 1013 cm-3 with a small
- With a full size sapphire crucible, growth of multi-layer
structured devices will be possible.
- Controlled doping of n-GaAs (e.g. with Te) is proven.
Verification of the reproducibility of the growth process
and manufacture of a BIB pilot sample, Fig. 2, are the next goals.
GaAs centrifuge growth system at UCB
© Infrared and Submillimeter Astronomy Group at MPE
28/10/2004, editor of this page: Thomas Ott