| Summary: | 碩士 === 國立交通大學 === 電子物理學系 === 85 === To combine the photo-electro properties of the low
temperature(LT) GaAs andthe superlattice structure, we used the
molecular beam epitaxy system to growthe LT InGaAs/GaAs
superlattice p-i-n structure. For comparison, the samples of the
smae struectures were grown at normal temperature. We continued
the research of the LT GaAs n-i-n and p-i-n structures to the
electrical and deep-level measurements on the LT InGaAs/GaAs
superlattice sample. The results we obtained are stated below.
In the current-voltage(I-V) measurement, we observed that the
leakage current of the LT sample was more than one order of
magnitude higher than thatof the reference samples. A smimilar
result was observed in our research of theLT GaAs p-i-n
structure. It was due to the high concentration of defects in LT
GaAs. Besides, at low temperarure, the LT sample had much higher
turn-on voltage than the reference samples. Yet we have not
found the suitable modelto explain the mechanism. Three deep
levels were observed in DLTS as well as admittance spectroscopy
for the LT sample. We labeled them as 91H, 91E1, and 91E2.
The activation energy and corss section of 91H are 0.71eV and
1.7x10^-11cm^2.Similar deep levels as 91H were also observed in
the reference samples. Therefore, this deep level was not
created by the LT growth and was speculated to be the result of
the lattice mismatch between InGaAs and GaAs. The activation
energy and cross section of 91E2 are 0.71eV and 1.5x10^-15cm^2.
This deep level was speculated to be EL2 because of its position
in the Arreheniusplot and quenching effect. The activation
energy and cross section of 91E1 are 0.46eV and 1.0x10^-16cm^2.
It was not observed in the reference samples, suggesting that it
is the uniquedeep level in the LT InGaAs/GaAs superlattice
layers. The position of this deep level in the Arrehenius plot
is in the vicinity of the dominating trap, 0.66eV,commonly
observed in LT GaAs. This deep level may play a similar
dominatingrole as the 0.66eV trap does in LT GaAs. Finally we
observed unusual negative capacitance under high reverse bias or
high temperature in our referencer samples by admittance
spectroscopy. From theliterate, the negative capacitance is
caused by the transient current. In the LT sample, there was no
negatice capacitance but the capacitance increased withfrequency
in the low frequency range. An activation energy obtained by
takingthe inflexion points of the capacitance-frequency(C-F)
curves in the low frequency range was found to correspond to
91E1. So, this deep level, 91E1, had a direct influence on the
transient current of the LT InGaAs/GaAs superlattice sample.
|
|---|
