The integration of an injection semiconductor laser with an active electronic device (Gunn oscillator) in a single epitaxial crystal device is demonstrated

Lee, C. P.

Margalit, S.

Ury, I.

Yariv, A.

English

Caltech Authors - Main

Downloaded 24 May 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp
Integration of an injection laser with a Gunn oscillator on 
a semi-insulating GaAs substrates> 
C. P. Lee, S. Margalit, I. Ury, and A. Yariv 
California Institute of Technology, Pasadena, California 91125 
(Received 21 February 1978; accepted for publication 6 April 1978) 
The integration of an injection semiconductor laser with an active electronic device (Gunn oscillator) in a 
single epitaxial crystal device is demonstrated. 
PACS numbers: 42.82.+n, 85.40.Gn, 85.30.Fg 
Integration of a variety of optical and electronic 
components monolithically on a single chip of substrate 
is the goal of integrated optics. During the past few 
years a lot of effort has been put into the development of 
individual optical devices such as low-threshold single-
mode GaAs lasers, waveguides, modulators, etc. 1 On 
the other hand, a great amount of progress has also 
been made on the high-speed GaAs electronic devices 
such as FET's, 2 Gunn oscillators, 3 etc. However, the 
integration of these two kinds of devices has not been 
achieved. Recently, we succeeded, for the first time, 
in fabricating GaAs heterostructure lasers on semi-
insulating substrates. 4•5 Because of the nonconductive 
substrate, the electrical integration can be performed 
on epilayers, and hence becomes much easier o In this 
paper we report, for the first time, the integration of 
a GaAs -GaAlAs injection laser with an electronic de-
vice -Gunn oscillator -on the same chip of substrate. 
The structure of the device is shown in Fig. 1. The 
laser has structure similar to our crowding effect 
laser4 except that the n-type layers are below the 
p-type layers. Current injected through then-type 
contact flows through the n-GaAs layer into the mesa 
regiono Due to the sheet resistance of the n-GaAs and 
n-GaAlAs layers, the voltage drop across the p-n 
junction decreases with distance from the edge of the 
mesao This causes the injected current to cross the 
p -n junction in a narrow stripe adjacent to the edge of 
the mesao This current crowding yields a narrow 
effective gain region near the mesa edge. When lasing, 
the near-field pattern (Fig. 2) shows that the laser 
light comes from a region only about 5 iJ.m wide. The 
Gunn device was fabricated on the first n-GaAs layer. 
As the voltage drop across the Gunn electrodes is 
higher than some critical value, a high -field dipole 
domain is formed and drifts from the cathode to the 
SEMI-INSULATING GaAs 
FIG. 1. The structure of the integrated Gunn-laser device. 
The voltage was applied between the cathode of the Gunn oscil-
lator and the p-type contact on top of the laser mesa. 
a>work supported by the National Science Foundation and the 
Office of Naval Research. 
anode. The frequency of oscillation depends on the 
distance between the electrodes and is higher as the 
distance is smaller. In our experiment the electrode 
on the left side of the Gunn device was not used, and 
the voltage was applied between the electrode to the 
right and the p -type contact on top of the laser mesa. 
The Gunn current thus flowed through the laser. If this 
current oscillation range is higher than the threshold 
of the laser, the laser light will be modulated. If the 
lasing threshold is between the upper limit and the 
lower limit of the current oscillation, 100% depth of 
laser light modulation can be achieved. 
The device consists of five epitaxial layers grown on 
a semi-insulating substrate. The first n-GaAs layer is 
used for fabricating the Gunn device and for providing 
the voltage drop for the crowding effect. The doping 
concentration of this layer was chosen to be - 1016 cm· 3 
in order to get a proper Gunn oscillation. The active 
layer of GaAs is not intentionally doped. The confining 
Ga1.xAlxAs layers have x- 0. 4 and are doped with Ge 
and Sn for p -type and n-type doping, respectively. The 
typical thicknesses of the layers, starting from the 
bottom, are 3, 2, 0. 3, 2, and 1 11m. The step etching 
was performed after the p-type contact (Au-Zn) was 
evaporated on the wafer. The etching has to be deep 
enough to reach the first n-GaAs layer. Following the 
etching step, then-type contact (Au-Ge) was evaporated. 
Using the step of the mesa as the self-aligned mask, 
we were able to evaporate Au-Ge on the n-GaAs layer 
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DISTANCE 
FIG. 2. The recorded traces of the near-field patterns of the 
laser at different currents. The threshold is 170 rnA. 
806 Appl. Phys. Lett. 32(12), 15 June 1978 0003-6951/78/3212-0806$00.50 © 1978 American Institute of Physics 806 
Downloaded 24 May 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp
FIG. 3. A four-trace oscillogram of the current and the light 
pulses. Trace 1 is the light pulse and trace 2 is the current 
pulse. Traces 3 and 4 are the expanded traces of 1 and 2, 
respectively. The time scale is 100 nsec/div for 1 and 2 and 2 
nsec/div for 3 and 4. 
with a separation between the contact and the step 
edge. A distance of 200 jJ.m to the right of the step 
edge, a 140-jJ.m-wide stripe window was opened in the 
Au-Ge contact using photolithographic methods. The 
GaAs(n) under the window serves as the drift region of 
the Glinn oscillator. The cross section of the final 
structure is shown in Fig. 1. As a two-terminal de-
vice, the voltage was applied across the p -type contact 
on the mesa top and the n-type contact on the far right. 
The laser (the laser is one of the Gunn oscillator elec-
trodes) and the Gunn device are thus integrated in 
series. The oscillating current pulses coming from the 
Gunn device form the injection current of the diode 
laser and modulate the laser light. The frequency of 
oscillation can be adjusted by changing the distance 
between the electrodes of the Gunn device. Direct 
current modulation of the light output at frequencies 
up to 1 GHz has been achieved. Figure 3, for example, 
is a four-trace oscillogram of the current pulse and 
the light pulse. Trace 1 is the light pulse and trace 2 
is the current pulse. Oscillation can be seen on top of 
both pulses. In this case even the minima of the cur-
rent exceed the threshold value (170 rnA) and the laser 
is not turned off. Because of the threshold nonlinear 
behavior of lasers, the modulation depth of the laser 
output (70%) is much larger than that of the current 
(15%). Traces 3 and 4 are expanded traces of the light 
and the current, respectively. The frequency of oscilla-
tion is about 0. 75 GHz. 
For three-terminal operation it is possible to put a 
Schottky gate on the Gunn device and use the gate to 
trigger the Gunn oscillation, In this way a single short 
laser pulse can be achieved. 
In conclusion, we have demonstrated the integration 
of an active electronic device, a Gunn oscillator in this 
case, with a GaAs laser on the same piece of semi-
insulating GaAs substrate. Direct current m"odulation 
on the light output has been achieved at frequencies up 
to 1 GHz. Further integration of the GaAs laser with 
other devices is in progress. 
1P. K. Tien, Rev. Mod. Phys. 49, 361 (1977). 
2C. A. Liechti, IEEE Trans. Microwave Theory Tech. 
MTT-24, 279 (1976). 
3K. Mause, A. Schlachetzki, E. Hesse, and H. Salow, 
IEEE J. Solid State Circuits SC-10, 2 (1975). 
4C. P. Lee, S. Margalit, and A. Yariv, Appl. Phys. Lett. 
31, 281 (1977). 
5C. P. Lee, s. Margalit, I. Ury, and A. Yariv, Appl. Phys. 
Lett. 32, 410 (1978). 
Low-resistivity ZnCdS films for use as windows in 
heterojunction solar censa> 
N. Romeo, G. Sberveglieri, and L. Tarricone 
Istituto di Fisica, C.N.R., G.N.S.M., Parma, Italy 
(Received I February 1978; accepted for publication 7 April 1978) 
Low-resistivity Zn,Cd1_,S films have been obtained by a multisource evaporation method. The films have 
been doped with In during the deposition. The resistivity of such films varies from 2X w-3 !lcm for x = 0 
up to 2 !lcm for x = 0.3 and rises up to 1012 !lcm for x =I. For energies lower than the energy gap, the 
transparency of these films, when corrected for the reflection loss, can reach a value of almost 100%. In 
the range of an x variation between 0 and 0.4 these films, because of their low resistivity and their high 
transparency, can be used as windows in heterojunction solar cells. 
PACS numbers: 73.60.Fw, 72.40.+w, 78.65.-s, 84.60.Jt 
In heterojunction solar cells, the part of the cell 
which serves as a window should have the highest 
forbidden gap possible and at the same time should have 
a very low resistivity. In some heterojunction solar 
cells, 1- 3 CdS has been successfully used as a window. 
This is due to the fact that CdS has both an high gap 
a) work supported by C. N. R. under the "Progetto Finalizzato 
Energetic a". 
of 2. 4 eV and a very low resistivity up to 10-2 n em or 
less in the form of films. 4- 6 ZnsCd1_sS films, if made 
807 Appl. Phys. Lett. 32(12), 15 June 1978 0003-6951/78/3212-0807$00.50 © 1978 American Institute of Physics 807 


Integration of an injection laser with a Gunn oscillator on

a semi-insulating GaAs substrates

https://authors.library.caltech.edu/32844/1/LEEapl78b.pdf

Integration of an injection laser with a Gunn oscillator on a semi-insulating GaAs substrates

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