Electrical Characterization of in Schottky Contacts to Epitaxial n-In 0.46 Ga 0.54 P Grown on n + -GaAs by Mocvd
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te its characteristic parameters"'9 . The 1 MHz C' 2-V/T data is analyzed in terms of the MIS 4 diode model of Hattori et aL 10 and the temperature dependence of bois established. EXPERIMENTAL TECHNIQUE Before deposition of metal contacts, the n-In0 .46Gao.54P/n+-GaAs samples were degreased with acetone and methanol at 350 C for 10 min., rinsed with deionized (DI) water and dried with Argon. To remove the native oxide, the samples were then chemically etched with HCI : H20 (1:1) solution at room temperature for 10 min., rinsed with DI water and dried with Argon. To obtain ohmic contact, In metal was thermally evaporated on the unpolished surface of n÷-GaAs, followed by a 10 min. anneal in vacuum at 3600 C. An In/n-In 0.46Ga0 .54P Schottky contacts of area 2.0x10-2 cm"2 was fabricated by thermal deposition of In onto the chemically etched surface of epitaxial n-Ino.46 Gao.54 P layer.
The In/n-In0 .46Ga0 .54P Schottky diode was mounted in a liquid-nitrogen cryostat and its temperature (T) was controlled and measured by a Stanton Red Croft 706 temperature programmer. The I-V characteristics were measured using a Keithley 480 picoammeter and a Keithley 617 electrometer. The 1 MHz C-V measurements were made using a Boonton 72B capacitance meter. The bias voltage was supplied by a EG&G PARC 175 voltage programmer. EXPERIMENTAL DATA AND ANALYSIS I-V/T Measurements
The forward I-V characteristics of the
In/n-Ino. 4 6Gao.5 4 P
Schottky diode were measured over
the temperature range 260-400 K. The {f/(]-exp(-qV/kT))} vs V plots at different temperatures shown in Fig. 1 are linear over the entire voltage and temperature range of our experiments showing that the series resistance effects were not important, The I-V data shown in Fig. 1 (discrete points) fitted very well to Eq. (3.13) in Ref 11 (Fig. 1, solid lines) with the values of the ideality factor (n) listed in Table I. The ideality factor varied between 1.26 and 1.78 over the temperature range 400-260 K (Table I).The non-ideal character in the forward I-V characteristics was introduced by the presence of an interface layer between the metal and semiconductor as well as by the participation of various current transport mechanisms. Following the non-linear curve fitting procedure reported elsewhere8 9, the experimental direct I-V values of the In/n-In0 .46Ga0 .54P Schottky diode were fitted to the relation (1)
1=11 + 13
where 13is the current due to the generation-recombination (GR) mechanism described by the Eq. (5) in Ref 8, 11the current due to the thermionic emission (TE) mechanism given by I,=1I[exp(qV/kT)-1]
(2)
the TE reverse saturation current, Io is defined by
with
Io=AA~ffT2exp[-q(4oo -A4bbo)/kT]
(3)
A~fr=A'exp(o3/k)
(4)
438
and
(5)
ýo= ý.oo- PT
where A is the area of the Schottky contact, q the magnitude of the electron charge, A** the modified effective Richardson constant which includes the effect of interface layer12, 46bo the zero bias barrier height, 600 the zero bias zero temperature barrier height, 3 the temperature coefficient of the z
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