High-quality Resonant Tunneling Diodes have been fabricated and tested as sources for millimeter and submillimeter wavelengths. The devices have shown excellent I-V characteristics with peak-to-valley current ratios as high as 6:1 and current densities in the range of 50-150 kA/cm(exp 2) at 300 K. Used as local oscillators, the diodes are capable of state of the art output power delivered by AlGaAs-based tunneling devices. As harmonic multipliers, a frequency of 320 GHz has been achieved by quintupling the fundamental oscillation of a klystron source

Beaudin, G.

Bockenhoff, E.

Bouregba, R.

Encrenaz, P.

Lippens, D.

Mounaix, P.

Nagle, J.

Palmateer, L.

Pernot, J. C.

Vanbesien, O.

English

NASA Technical Reports Server

Page 548 Third International Symposium on Space Terahertz Technology
N 9 3 - 2 7 7 7 2
RESONANT TUNNELING DIODES AS
SOURCES FOR MILLIMETER AND
SUBMILLIMETER WAVELENGTHS
O. Vanbesien, R. Bouregba, P. Mounaix
and D. Lippens
Centre Hyperfrequences et Semiconducteurs U.A. CNRS N° 287
Universite de Lille - 59655 Villeneuve d'Ascq Cedex - France
L. Palmateer+, J.C. Pernot, G. Beaudin*
and P. Encrenaz
Ecole Normale Superieure 24, rue Lhomond 75231 PARIS
* Observatoire de Meudon 92195 Meudon Principal Cedex
E. Bockenhoff + +, J. Nagle, P. Bois, F. Chevoir
and B. Vinter
Laboratoire Central de Recherche Thomson CSF
Domaine de Corbeville 91404 Orsay Cedex - France.
ABSTRACT
High-quality Resonant Tunneling Diodes have been fabricated
and tested as sources for millimeter and submillimeter
wavelengths. The devices have shown excellent I-V characteristics
with peak-to-valley current ratios as high as 6:1 and current
densities in the range of 50-150 kA/cm2 at 300 K. Used as local
oscillators, the diodes are capable of state of the art output power
delivered by AlGaAs-based tunneling devices. As harmonic
multipliers, a frequency of 320 GHz has been achieved by
quintupling the fundamental oscillation of a klystron source.
+
 Now at IBM, Yorktown Heights + + at Mercedes Benz, Stuttgart
https://ntrs.nasa.gov/search.jsp?R=19930018583 2020-03-17T05:43:30+00:00Z
Third International Symposium on Space Terahertz Technology Page 549
1. INTRODUCTION
Resonant Tunneling Diodes (RTD's) exhibit very strong non linearity with
short time response which make them attractive in non linear applications for
millimeter and submillimeter wavelengths [1]. RTD's have already demonstrated
their potential for a variety of high speed/high frequency applications [2]-[5]. In
this paper we report on the effort of a group of laboratories in France on these
novel devices with special emphasis on local oscillators and harmonic multipliers.
The fabrication procedures in a whisker contacted technology and in a microwave
compatible technology suitable for monolithic integration are outlined in section
2. The DC and AC characterizations are reported in section 3 whereas the
oscillator and multiplier results using the devices are described in section 4.
2. TECHNOLOGICAL PROCESS
The two types of epitaxial structures grown by molecular beam epitaxy are
given in Figure l(a) and (b). Both samples noted A and B had 17 A - thick AlAs
barriers and access regions with a stepped doping profile from l-2x!01'7 cm-3 to 2-
3x1018 cm-3. They differ mainly owing to the strained Gao.glno.iAs layers so that
structure B resembles a triple well resonant tunneling structure. By placing a
GalnAs well just prior the growth of the double barrier heterostructure (DBH) it
is expected that the peak-to-valley current ratio (PVCR's) should be enhanced
because the negative differential resistance effect involves the anticrossing of two
confined states [6] [7]. In addition by placing a GalnAs well rather than a GaAs
one and by a proper choice of the well width (Lw = 40 A), the ground state can be
lowered in energy while keeping the excited state practically unchanged. The
associated benefits are a reduction of the peak voltage and higher PVCR's [8].
Also note that structure A and B are grown on n+ and S-I substrates respectively.
Page 550 Third International Symposium on Space Terahertz Technology
GaAs
GaAs
GaAs
AlAs
GaAs
AlAs
GaAs
GaAs
GaAs
2 1013cm-3
2 1017cm-3
undooed (UD)
UD
UD
UD
UD
2 1017cm"3
2 1018cm-3
490 nm
50 nm
5 nm
1.7 nm
4.5 nm
1.7 nm
5 nm
50 nm
500 nm
(a)
n+ substrate
GaAs
GaAs
GaAs
In i Ga9 As
GaAs
AlAs
GaAs
In.iGa.gAs
3 1018cm-3
1017cm-3
undoped (UD)
UD
UD
UD
UD
UD
500 nm
10 nm
5 nm
5 nm
0.5 nm
1.7 nm
0.5 nm
4 nm
Symmetrical layers
(b)
Figure 1 :Growth sequence for the epilayer on n+ substrate (sample A), (a)
Sample B grown on semi-insulating subtrate. (b)
The epilayers on n + substrate were processed using a whisker contacted
technology including patterning of Ni/GeAu layers into matrix of 3.5 um diameter
dots on the epitaxial side of the wafer and uniform deposition on the back side
followed by alloying of these layers to make ohmic contacts. Mesa isolation was
performed by chlorine ion beam assisted etching as shown in figure 2, using the
patterned metal as a mask. As last stages some of the samples were thinned to a
thickness of about 120 um and polyimide was used to surround the diodes in order
to aid whisker contact.
Third International Symposium on Space Terahertz Technology Page 551
Figure 2 : SEM Photos of diodes formed by RIE.
For the epilayers on S-I substrate, the diodes were fabricated in a
microwave-compatible two-step mesa technology [9]. In that case, the devices
were connected to low-loss transmission lines in such a way that they can be
characterized at the wafer level. Such vertically integrated devices require a
means of connecting the contact on the top of the mesa to the pad of the
transmission line. We thus developed two versions : (i) a dielectric assisted cross-
over and (ii) an air bridge interconnection. A scanning electron micrograph of two
representative devices are shown in figures 3 and 4. In figure 3 a coplanar probe
configuration is apparent. Also clearly shown is the deposited strap which crosses
over the mesa edges covered with Sis N4 layer appearing in dark. In the second
version, the dielectric cross-over is replaced by an air bridge yielding a reduced
parasitic capacitance. Figure 4 illustrates the technology employed with the
Page 552 Third International Symposium on Space Terahertz Technology
mushroom shaped metallization which enables one to connect small anode
fingers.
AuGeNi Ohmic Contacts
Overlay Metallization
FigureS .-Schematic cross section and SEM photo of the RTD fabricated in a
planar technology.
Figure 4 : SEM of a diode fabricated using air bridge techniques.
Third International Symposium on Space Terahertz Technology Page 553
3. DC AND AC CHARACTERIZATION
Figure 5a shows a typical current voltage I-V characteristic for a GaAs/AlAs
device on n+ substrate at 300K. The device exhibits a peak current of — 16 mA at
— 1.8 V which corresponds to a peak current density of— 160 kA/cm2 for a 3,5 um
diameter diode. For larger size of the diodes, heating of the samples prevents us
from achieving these densities. A typical DC characteristic for a device on SI
substrate is displayed in Figure 5b. The device exhibits excellent characteristics
with PVCR's as high as 6:1 along with simultaneously peak current density of
50 kA/cm2 which compare favorably to the best published results [10] [11] Note
also the high degree of symmetry in the I-V curve which is a good indicator of
quality interfaces.
20
16
< 12
E 8
4
1 0
1-4
-12
-16
-20
T-300K
- 2 - 1 0 1
Voltage V
8
6
< 4
2
r2I-4
-6
-8
T-300K
-U5 -.8 0 .8
Voltage V
U6
Figured .-Typical DC characteristics for a GaAs/AlAs device on n+ substrate (a)
and for a GalnAs/GaAs/AlAs pseudomorphic device on SI substrate (b).
Page 554 Third International Symposium on Space Terahertz Technology
Following our previous work [12], on-wafer reflection gain measurements
were performed between 50 MHz and 40 GHz using cascade RF probes and an
85107 A HP network analyser. Shown in Figure 6 is the one port measurement of
a vertically integrated sample. The active area is 20 um2. The diode is biased in
the NDR region. Note that ho de-embedding was used at this stage to correct for
parasitics. For frequency evaluation, we used the equivalent circuit which
consists of a single capacitor Cd with a parallel negative resistance Rd- -hese
intrinsic lumped elements are completed by the parasitic capacitance Cp, the
inductance Lp attributable to the bonding and Rs the overall series resistance. A
good fit was obtained for Cd = 36 fF, Rj = - 172 Q, Rs = 9 Q, Lp = 60 pH and
Cp = 13 fF (air-bridge technology). With this set of data derived from experiment,
the cut off frequency for NDR is in excess of 100 GHz. This frequency is limited by
the high impedance level needed to satisfy the stability criteria.
2.5 Units
900.0 iriJnit*/
-30.09 Q -92.191 Q
A MARKER
40.
START 0.050000000 GHz
STOP 40.000000000 CMz
Figuer 6 :One port measurement of the impedance. The bias is adjusted in the NDR
region to satisfy the stability criteria.
Third International Symposium on Space Terahertz Technology Page 555
4. OSCILLATOR AND MULTIPLIER RESULTS
The wafers on n+ substrate were sawed into chips of 100x100 um2 and
mounted in a test waveguide for measuring the oscillator power at 35 and 110
GHz. The power levels measured at 300 K with a bolometer were 36 uW at 38.6
GHz and 12 uW at 110 GHz. Referring to the oscillator results from the published
literature on AlGaAs based RTD's [13] given in figure 7 the output power are
state of the art results.
100.
I
10
0.1
.EXPERIMENT
• Sollneretal
- A our work
I I I I II II I I I I I Illl I I I I I III
1 10 10O
Frequency GHz
1000
Figure 7 .-Experimental powers for a 4 um diameter diode from reference 113] and
results from the present work for a 3.5 um diameter diode.
For harmonic multiplication, the samples were mounted in a commercially
available multiplier mount. The measurement set up has a quasi-optical scheme
and was initially developed to study reactive species of astrophysical interest [14].
The diodes were driven by a klystron at 64 GHz and, in the output path, high
filters enables one to spectrally analyze the power delivered by the diode. The
receiver is a helium cooled InSb detector. Figure 8 shows the power response at
3rd harmonic (192 GHz) and 5th harmonic (320 GHz). For comparison in terms of
available power commercial Schottky diodes were also tested under the same
Page 556 Third International Symposium on Space Terahertz Technology
experimental conditions. It is interesting to note that equivalent performances
were obtained for both types of devices by increasing the multiplication order to
frequency quintupling.
SCHOTTKY fifth harm.
500
 T
400 --
Og
UJfc
O
IU
o
t
300 --
200 --
100 --
OBRTD third harm.
• *
•
DBRTD ftftft harm.
.';/
+ 4*^1
16 14 12 10 8 6 4 2 0
POWER SOURCE ATTENUATION (dB)
Figure 8 .'Measured voltage of InSb detector against input power delivered by a
klystron at 64 GHz.
Third International Symposium on Space Terahertz Technology Page 557
In the multiplier experiment the devices were unbiased and driven in the
NDR region to take advantage of multiple extrema in the current waveform. This
requirement can be unfavorable especially for high threshold voltage devices
when input power is limited [14]. From this viewpoint, it is clear that
pseudomorphic structures with a buried well may overcome partly this difficulty.
From Figure 3 it is apparent that a drastic decrease in the peak voltage 0.8 V
instead of 1.8 V has been achieved by comparing structures A and B. In addition it
can be noted that the PVCR's were enhanced. This suggests the superiority of
these new tunneling devices for multiplication in view of the large harmonic
content in the current and of the reduction of the amount of input power required
to pump the diode.
5. CONCLUSION
High performance resonant tunneling diodes were sucessfully fabricated in
a whisker contacted and in a planar technology. The RF capabilities of the diodes
were demonstrated either by direct measurement of their small-signal impedance
or by using them for oscillator and multiplier.
ACKNOWLEDGEMENTS
This work was supported by the Ministere de la Recherche et de la
Technologic. Technical assistance of M. Bogey, J.L. Destombes and A. Lescluse
with the Laboratoire de Spectroscopie Hertzienne of the Lille University is highly
appreciated.
Page 558 Third International Symposium on Space Terahertz Technology
REFERENCES
[1] T.C.L.G- Sollner, E.R. Brown and H.Q. Le, "Microwave and Millemeter-
wave Resonant Tunneling Devices". Physics of Quantum Electron Devices
edited by F. Capasso Springer-Verlag.
[2] E.R. Brown, J.R. Soderstorm, CD. Parker, L.J. Mahoney, K.M. Kolvar and
T.C. Me Jill, "Oscillations up to 712 GHz in InAs/AlSb resonant tunneling
diodes". Appl. Phys. Lett. 58, pp. 2291-2293, May 1991.
[3] A. Rydberg and H. Gronquist "Quantum well high efficiency millimeter-
wave frequency tripler". Electronics Letters, Vol. 25, pp. 348-349,1989.
[4] P.D. Batelaan and M.A. Frerking, "A quantum well frequency multiplier
with millimeter wave output". Proc. 4th Conf. Infrared Physics Zurich,
pp. 527-529,1988.
[5] R. Bouregba, D. Lippens, L. Palmateer, E. Bockenhoff, M. Bogey, J.L.
Destombes and A. Lecluse, "Frequency multiplication using resonant
tunneling diode with output at submillimeter wavelengths". Electronics
Lett. Vol.26, pp. 1804-1905, October 1990.
[6] D. Thomas, F. Chevoir, E. Barbier, Y. Guldner and J.P. Vieren, "Magneto
tunneling of charge build up in double barrier diodes". Proc. of 4th
International Conference on Superlattices Microstructures and
Microdevices 5, pp. 219-224,1989. .
[7] P. Mounaix, O. Vanbesien and D. Lippens, "Effect of cathode spacer layer on
the current-voltage characteristics of resonant tunneling diodes". Appl.
Phys. Lett. 57, pp 1517-1519, October 1990.
Third International Symposium on Space Terahertz Technology Page 559
[8] T.P.E. Broeckaert, W. Lee and C.G. Fonstad "Pseudomorphic
Ino.53Gao.47As/AlAs/InAs resonant tunneling diodes with peak-to-valley
current ratios of 30 at room temperature.
[9] D. Lippens, E. Barbier and P. Mounaix, "Fabrication of High-Performance
AlxGai-xAs/InyGai-yAs/GaAs Resonant Tunneling Diodes using a
Microwave-compatible Technology. IEEE Electron Dev. Lett. Vol. 12, pp.
114-116, March 1991.
[10] R.M. Kapre, A. Madhuka r , and S. Guha "Highly strained
GaAs/InGaAs/AlAs resonant tunneling diodes with simultaneously high
peak current densities and peak-to-valley current ratios". Appl. Phys. Lett.
58, pp. 2255-2257, May 1991.
[11] H. Brugger, U. Meiners, C. Wolk, R. Deufel, A. Morten, M. Rossmanith,
K.V. Klitzing and R. Sauer "Pseudomorphic Two Dimensional Electron-Gas-
Emitter Resonant Tunneling Devices" Microelectronics Engineering
Elsevier, 15, pp. 663-666,1991.
[12] P. Mounaix, P. Bedu, D. Lippens and E. Barbier "Measurement of negative
differential conductance up to 40 GHz for vertically integrated resonant
tunneling diodes". Electronics Letters Vol. 27, pp. 1358-1359, July 1991.
[13] E.R. Brown, T.C.L.G. Sollner, C.D. Parker, W.D. Goodhue and C. Chen.
"Oscillations up to 420 GHz in GaAs/AlAs resonant tunneling diodes" Appl.
Phys. Lett. 55, pp. 1777-1779, October 1989.
[14] J.L. Destombes, C. Demuynck and M. Bogey "Millimeter-wave and
submillimeter-wave spectroscopy of molecular ions". Phil. Trans. R. Soc. A
324, pp. 147-162,1988.


Resonant tunneling diodes as sources for millimeter and submillimeter wavelengths

Resonant tunneling diodes as sources for millimeter and submillimeter wavelengths

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server