Room temperature differential negative resistance in an
Al/Zn
0.61
Cd
0.39
Se/ n
-InP device
Kai Shum,
a)
J. Zhou, and W. Zhang
Department of Electrical Engineering, City College and Graduate Center of The City College of the City
University of New York, New York, New York 10031
L. Zeng and M. C. Tamargo
b)
Department of Chemistry, City College and Graduate Center of The City College of the City University of
New York, New York, New York 10031
Received 15 April 1997; accepted for publication 10 June 1997
Experimental data are presented on the current–voltage characteristics of an Al/ZnCdSe/ n
+
-InP
device from 77 to 300 K. A strong negative differential resistance under forward bias was observed
for temperature higher than 145 K. The peak-to-valley current ratio was measured to be 30 at room
temperature. In the reverse bias region the device behaves as a leaky Schottky diode. © 1997
American Institute of Physics. S0003-69519702432-7
Nearly lattice-matched ZnCdSe/ZnCdMgSe quantum
well structures have been recently grown on InP substrates
by molecular beam epitaxy MBE. The photoluminescence
study
1
shows that emission from these structures can cover
the whole visible spectral region from blue to red giving a
possibility of fabricating full color displays. Quantum carrier
confinement near the ZnCdSe/InP heterointerface was
observed
2
using the capacitance–voltage ( C – V ) technique.
From this observation it was unambiguously shown that the
energy band of InP is staggered to that of ZnCdSe type II
band alignment. It is important to understand how effi-
ciently electrons can be injected to an active region from an
n
+
-InP substrate for a successful realization of practical de-
vices based on ZnCdMgSe/InP materials. In this letter, we
report on the current–voltage ( I – V ) characteristics of an
Al/ZnCdSe/ n
+
-InP device from 77 K to room temperature.
A strong negative differential resistance NDR under for-
ward bias was observed for temperature higher than 145 K.
The peak-to-valley current ratio at room temperature was
measured to be 30. In the reverse bias region the device
behaves as a Schottky diode. NDR devices based on resonant
tunneling in double-barrier structures have attracted much
interest since the pioneering work of Tsu, Esaki, and Chang.
3
This new observation may render II–VI semiconductor com-
pound structures grown on InP substrates technologically
useful for millimeter-wave applications.
The Zn
x
Cd
1 -x
Se/InP heterostructure studied in this
work was grown on an n
+
InP001 substrate in a Riber
2300P MBE system consisting of two growth chambers, one
for the growth of III–V’s and the other for the growth of
II–VI layers, coupled by ultra high vapor UHV transfer
chambers. Detailed growth conditions and the substrate
cleaning method were described previously.
1
The epitaxy
structure consists of a 1.080.02 m layer of Zn
x
Cd
1 -x
Se
and a 50 nm InP buffer layer. Both layers were intentionally
undoped. However, the background doping level is about
10
17
– 10
18
cm
-3
for InP and 10
14
– 10
15
cm
-3
for
Zn
x
Cd
1 -x
Se as measured by the Hall effect in samples
grown under similar conditions. The layer thickness of
ZnCdSe was measured by grooving the sample with a Philtec
sectioner and the thickness of InP is estimated by the growth
rate. The ZnSe fraction x =0.61 was determined
2
from single
crystal x-ray diffraction. Schottky diodes were fabricated by
depositing round-shaped Al contacts with a thickness of
3000 Å and a diameter of 2 mm using a high vacuum e -beam
evaporator through a mask onto the Zn
0.61
Cd
0.39
Se epilayer.
Individual diodes were then cleaved from the wafer and
bonded to a device holder for both I – V and C – V measure-
ments. For low-temperature measurements, the device was
placed onto the cool finger of a cryostat. The I – V data were
taken by a computerized HP4142B source/monitor unit.
Figure 1 shows the I – V characteristics obtained from
one of our devices measured at room temperature. This de-
vice was also used for C – V measurements as reported in
Ref. 2. Three features in this I – V curve can be observed.
First, there is an obvious strong resonant peak at V
p
=0.554 V with a peak current value of I
p
=3.57 mA and a
deep valley at V
v
=0.605 V with a valley current of I
v
=0.12 mA. The peak-to-valley current ratio ( =I
p
/ I
v
) is
a
Electronic mail: shum@ee-mail.engr.ccny.cuny.edu
b
Electronic mail: tamar@scisun.sci.ccny.cuny.edu
FIG. 1. Current–voltage curve of the Al/ZnCdSe/InP(50 nm/ n
+
-InP(2
10
18
cm
-3
) device at room temperature. The peak-to-valley current ratio
is 30. The inset is a sketch of the energy band diagram of the device struc-
ture.
815 Appl. Phys. Lett. 71 (6), 11 August 1997 0003-6951/97/71(6)/815/2/$10.00 © 1997 American Institute of Physics