PROJECT DETAILS
| Name: |
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Preparation of the radiation resistant solar cells from GaInP2/GaAs |
| From: |
|
2002-08-01 |
|
| To: |
|
2004-12-31 |
Full optimisation of the GaInP2/GaAs growth conditions has been realized in more
than 500 growth experiments at the growth temperature app. 790oC, with the
initial supercooling 6-15 oC in the graphite boat cooled down with the rate
app. 0.5oC/min, placed into horizontal furnace. The optimised composition melts
were prepared in advance in the special dosing boat. In terms of the LPE growth
of multicomponent solid solution, the melt during homogenisation has been
“single phase” and growth process has been realized in the “supercooling” variant.
The unintentionally doped layers grown at the optimised conditions show low
temperature PL spectra characteristic with the presence of bound excitonic line
(BE) with maximum at 1.981 eV . Accounting the calculated value for the BE
binding energy of ~5 meV for the band-gap energy in our samples we obtain
~ 1.986 eV. The FWHM of the BE line is 7 meV, which very close to the value
estimated theoretically on account of the compositional fluctuations in GaInP.
Origin of the specific defects observed and than eliminated in GaInP on GaAs
as well as GaAs on InGaP have been identified. “Gross shift” in GaAs-melt
composition grown on GaInP, (related to melt carry over), produces an ordered
or disordered dislocation network areas. Transition between ordered and
disordered areas is typically sharp and when melt carry over is higher, ordered
areas produce sharply bounded islands. Morphological study is well documented
by microphotographs of the structures.
To grow the p-type GaInP, a new doping method has been investigated. Instead of
the highly volatile Zn impurity, which contaminates another melts, Mg has been
used. Observed acceptor concentration was in the range 1.2*1017 – 1.8*1019 cm-3.
A GaInP layer doped by manganese demonstrate p-type conductivity up to
6*1017 cm-3 with adverse influence of the Mn on the layers morphology and PL
intensity. Adding 0.03 at% of Er to the unintentionally doped melt results in a
reduction of the donor concentration to 1.5*1015 cm-3. The electron concentration
in this layer decreases by several orders of magnitude as the temperature
decreases to 10 K. The best quality GaAs on GaInP structures have been observed
when GaAs layers were grown from the Bi melt.
