Semiconductor device having two intersecting sub-diodes and transistor-like properties

A semiconductor device is disclosed in which an intrinsic or weakly doped semiconductor layer is arranged on a substrate. The semiconductor layer contains a first P doped zone and a first N doped zone which are separated by a portion of the said intrinsic layer serving as base zone. The semiconductor layer further contains a second P doped zone and a second N doped zone which are also separated from one another by the base zone. The four doped zones are arranged such that a connecting line between the second P doped zone and second N doped zone intersects a connecting line between the first P doped zone and the first N doped zone preferably at right angles. A sub-diode formed of the first doped zones affects the operation of a sub-diode formed by the second doped zones.

BACKGROUND OF THE INVENTION 
The invention relates to a semiconductor device having an intrinsic or 
weakly doped semiconductor layer containing a P doped zone and a N doped 
zone separated by an intrinsic or weakly doped base zone. 
Bipolar transistors and field effect transistors are known semiconductor 
devices. In semiconductor thin-film technology, bipolar transistors can be 
constructed as so-called "lateral transistors". In this technology it is 
difficult to produce sufficiently short base zones. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a bipolar semiconductor device or 
component having transistor-like properties, which is suitable for 
construction in thin-film technology. 
According to the invention, a semiconductor device is formed of an 
insulating or weakly conductive substrate with an intrinsic or weakly 
doped semiconductor layer arranged on the substrate. First and second P 
doped zones and first and second N doped zones are formed in this 
semiconductor layer. Each of the zones is separated from the others by a 
portion of the semiconductor layer which serves as an intrinsic or weakly 
doped base zone. A connecting line between the second P doped zone and the 
second N doped zone intersects a connecting line between the first P doped 
zone and the first N doped zone. The first P and N doped zones form a 
first sub-diode and the second P and N doped zones form a second 
sub-diode. The operation of one sub-diode affects the operation of the 
other sub-diode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention is based on the following considerations: bipolar 
semiconductor components consist of a sequence of semiconductor layers 
exhibiting differing doping. Layer sequences of this type can easily be 
achieved in semiconductor wafers by diffusing in dopant from both 
surfaces. In the Planar technique, only one surface side of a 
semiconductor wafer, e.g. a silicon wafer, is processed. Thus, for 
example, there are both laterally constructed transistors and PIN diodes 
in the Planar technique. Structures of this type are particularly suitable 
for the thin-film technique. A lateral structuring can be two-dimensional, 
e.g. in accordance with FIG. 1, where 1 designates a substrate, in 
particular an insulating substrate, 2 designates a layer of semiconductor 
material, 3 designates a first P doped zone; 4 designates a second P doped 
zone, 10 designates an intrinsic or weakly doped base zone, 6 designates a 
first N doped zone and 5 designates a second N doped zone. On the doped 
zones 3, 4, 5, 6 metal layers 13, 14, 15, 16 are applied as ohmic contacts 
and are provided with supply lines. The construction illustrated therein 
can be considered as a construction of two side-by-side diodes, or as has 
been done below, as a pair of intersecting diodes, depending upon the 
manner in which the terminals are applied and connected. The pairs of 
zones 3, 6 and 4,5 are considered as sub-diodes. The base path between the 
two doped zones can be shorter than, equal to, or exceed the diffusion 
length of the charge carriers. When the distance between the P zone and 
the N zone of a sub-diode is great in comparison to the diffusion length 
of the charge carriers in the base zone 10 lying therebetween, such a 
sub-diode will be referred to as a "long" diode, and otherwise as a 
"short" diode. The electrical current flow through the intrinsic or weakly 
doped base zone 10 takes place by diffusion of the charge carriers in the 
case of "short" diodes poled in the forward direction, and takes place by 
a drift movement of charge carriers injected to the P or N conducting 
zones in the case of "long" diodes. The system consisting of the two 
intersecting PIN diodes or PSN diodes can consist of two "short" and also 
of two "long" diodes or a combination of a "long" and a "short" sub-diode. 
The significance of the four-pole structure is that the characteristics of 
the sub-diodes mutually influence one another. 
In a special embodiment of the invention, a "long" diode is combined with 
one (FIG. 2) or a plurality of e.g. two "short" diodes (FIG. 3). The 
asymmetrical form shown in FIG. 2 is used in particular when the 
intermediate area between the doped zones which represents the base zone 
10 is not intrinsic but is weakly doped. With the described arrangement of 
the intersecting diodes, the currents flowing through the two diodes 
mutually influence one another. When one "long" diode is combined with a 
plurality of e.g. two "short" or also "long" diodes, a structure is 
obtained which has a plurality of inputs (4, 5 and 8,) (FIG. 3). A further 
generalization of the diode intersection leads to a star-like arrangement 
of diodes which mutually penetrate one another. 
In the following the mode of functioning of the component corresponding to 
the invention will be explained in detail. 
First, a special mode of functioning of the component corresponding to the 
invention comprising two sub-diodes will be explained. A sub-diode to 
which a voltage U.sub.1 is connected and through which the current I.sub.1 
flows is referred to as an input diode. The other diode which is connected 
to the voltage U.sub.2 and through which the current I.sub.2 flows is 
considered as an output diode. The two currents I.sub.1 and I.sub.2 are 
dependent upon the two voltages U.sub.1, U.sub.2. We have: 
EQU I.sub.1 =G.sub.11 U.sub.1 +G.sub.12 U.sub.2, 
EQU I.sub.2 =G.sub.21 U.sub.1 +G.sub.22 U.sub.2 
or in brief 
EQU I=G.multidot.U 
where G.sub.11, G.sub.12, G.sub.21, G.sub.22 are the elements of a matrix 
G; these are functions of the two voltages U.sub.1, U.sub.2 resulting for 
U.sub.1 .fwdarw.0 in G.sub.11 U.sub.1 .fwdarw.0 and G.sub.21 U.sub.1 
.fwdarw.0 and with corresponding results when U.sub.2 .fwdarw.0. Currents 
and voltages in the forward direction (forward currents and voltages) are 
marked with a positive sign, whereas backward (reverse) currents and 
voltages are marked with a negative sign. Now the situation 
EQU U.sub.1 &gt;0, U.sub.2 &lt;0 (Equation 1) 
will be considered. The input will thus be considered to be poled in the 
forward direction, whereas the output will be considered to be poled in 
the backward direction. The input voltage U.sub.1 &gt;0 amplifies the output 
reverse current I.sub.2, which on account of U.sub.2 &lt;0, is I.sub.2 &lt;0. 
Likewise the output voltage U.sub.2 &lt;0 increases the input current I.sub.1 
which, on account of U.sub.1 &gt;0, is I.sub.1 &gt;0. Accordingly, G.sub.12 &lt;0 
and G.sub.21 &lt;0. It is to be assumed that these two effects maintain a 
balance. Thus 
EQU G.sub.21 U.sub.1 +G.sub.12 U.sub.2 =0 (Equation 2) 
Now, with a fixed input voltage U.sub.1, the currents I.sub.1 and I.sub.2 
for U.sub.2 .noteq.0 and U.sub.2 =0 are compared with one another. Thus it 
is necessary to distinguish G(U.sub.2) from G(0). Furthermore G.sub.11 
(0).apprxeq.G.sub.11 (U.sub.2) is set, and I.sub.2 (U.sub.2 =0)=G.sub.21 
(U.sub.2 =0).multidot.U.sub.1 .apprxeq.0 and G.sub.22 (U.sub.2)U.sub.2 
.apprxeq.0. Then from Equation 2 the equation 
EQU I.sub.1 (U.sub.2)-I.sub.1 (U.sub.2 =0)+I.sub.2 (U.sub.2)=0 (Equation 3) 
can be approximately obtained, where I.sub.1 (U.sub.2 =0) is determined by 
U.sub.1. 
The output reverse current I.sub.2 is fundamentally transferred from the 
input current I.sub.1. In order to illustrate Equation 3, the current 
transfer coefficient 
##EQU1## 
and the current amplification coefficent 
##EQU2## 
are introduced. 
A comparison of Equation 4 and Equation 5 indicates that 
##EQU3## 
Furthermore, since .vertline.I.sub.2 (U.sub.2).vertline.&lt;I.sub.1 (U.sub.2), 
it follows that: 0.ltoreq..alpha..ltoreq.1 and 
0.ltoreq..beta..ltoreq..alpha.. 
With a full current transfer of .alpha.=1, the current amplification is 
.beta.=.alpha.. With an absent current transfer .alpha.=0, the curent 
amplification also disappears, i.e., .beta.=0. For .alpha.=1/2, .beta.=1, 
i.e. .alpha.&gt;1/2 supplies .beta.&gt;1. A current amplification results in a 
power amplification when .vertline.U.sub.2 .vertline.&gt;U.sub.1 is chosen. 
In order to underline the similarity of the component corresponding to the 
invention with a bipolar transistor, in the following the input diode will 
also be referred to as an emitter diode and the output diode will also be 
referred to as a collector diode. The interaction between input and output 
takes place in that the holes and electrons injected via the emitter diode 
of the input are partially sucked away by the collector diode of the 
output. To enable a reasonable current response to take place, the 
injection must be effected directly into the space charge zone of the 
collector diode. In the ideal situation of an intrinsic base, the space 
charge zone would extend from the anode of the collector diode to the 
cathode. With a doped base, the voltage applied to the collector diode 
must be sufficient for the space charge zone commencing from a contact to 
reach the connection line between anode and cathode of the emitter diode, 
the "emitter axis". An asymmetrical structure as illustrated in FIG. 2 
meets this requirement. 
As shown in FIG. 1, the input circuit may include the forward bias U.sub.1 
connected in series with a control voltage U.sub.s between terminals 13 
and 16. The output circuit is a series connection of a reverse bias 
U.sub.2 and load R.sub.1 connected between terminals 14 and 15. 
In order to estimate the degree of current amplification, it is provided 
that .beta.=t.sub.1 /t.sub.2, where t.sub.1 signifies a minority carrier 
transit time between the emitter contacts (needed to cross the base region 
common with the collector diode) and t.sub.2 signifies the corresponding 
time for the collector contacts. A more precise estimation can be given 
for an arrangement consisting of two "long" diodes in the form 
##EQU4## 
Then the situation .beta.&gt;1 can easily be attained. Consequently, with an 
increasing reverse voltage, there is not only an increase in the current 
amplification but also a decrease in the switching time. 
In pulsed operation, the switching speed essentially corresponds to the 
time required to transfer the injected charge carriers. The dimensions of 
the base zone 10 are related to the diffusion length of the charge 
carriers and thus, in particular, to the carrier lifetime. Thus when the 
charge carriers have a low lifetime, correspondingly small dimension have 
to be chosen for the base zone 10 which has a favorable effect upon the 
switching speed. 
When the component corresponding to the invention is constructed in the SOS 
technology (silicon on sapphire), a distance of 10 .mu.m is already "long" 
i.e., considerably longer than the diffusion length of the charge 
carriers. Therefore, by designing the component corresponding to the 
invention in the SOS technology, very short switching times can be 
achieved. In SOS technology, the production of good lateral transistors is 
difficult since the requisite short base length of approximately 1 .mu.m 
cannot easily be preserved because of lateral diffusion. The component 
corresponding to the invention on the other hand has advantages because it 
is indeed capable of functioning in the case of comparatively larger base 
diameters. 
In the device corresponding to the invention, an additional field effect 
control of the potential distribution and of the space charge distribution 
and the carrier concentration distribution can be carried out which 
affects the current distribution and the current transfer. For this 
purpose, as shown in FIG. 4, a field effect electrode 21 is applied over 
an insulating layer 20. The field effect voltage can be applied between 
the terminal 22 and a (not shown) substrate contact, or also between 22 
and one of the base contacts 3, 4, 5 or 6. 
Another additional control possibility consists in connecting a magnetic 
field in parallel to the surface, so that the Lorentz force is at right 
angles to the surface. In this way, for example, the current between the 
contacts of an emitter diode can be brought deeper into the base volume so 
that the current transfer into the collector circuit reduces. 
The arrangement corresponding to the invention has here been represented as 
an input diode and an output diode which intersect with one another. In 
addition, simpler connection possibilities with conventional modes of 
functioning are possible. The interconnection of the two P contacts and 
the two N contacts produces a PSN diode. Naturally, one sub-diode will 
also be sufficient. In the case of a long base, a double injection diode 
is obtained. The application of a transversal magnetic field in parallel 
with the layer produces a magnetodiode. If, for example, a deeper 
semiconductor base exists, the injection current can be drawn downwards by 
the Lorentz force. The increase in the length of the current path then 
produces an increase of the resistance. In the case of a thin-film base, 
as occurs, for example, when the SOS technology is employed, a lifetime 
gradient extends into the semiconductor from the substrate surface towards 
the surface of the semiconductor layer. The Lorentz force can deflect the 
carriers either towards the substrate surface or towards the surface of 
the semiconductor layer. In the first situation the average lifetime is 
shorter than in the second situation. Therefore the double injection is 
impeded in the first situation but promoted in the second situation. In 
dependence upon the direction of the magnetic field, an extremely powerful 
positive or negative magnetoresistance is obtained. 
If, in an arrangement corresponding to the invention comprising a "long" 
and "short" diode (e.g. as in FIG. 2), a terminal of the short transverse 
diode is left open, a structure is obtained for example, where .pi. is a 
longitudinal base with injecting contacts at the opposite ends. A .pi.N 
junction is arranged transversely thereto. This arrangement can be 
understood and operated as a double-base diode. In diodes of this type, 
the base can be provided with ohmic contacts in the longitudinal 
direction, but also, as here, with injecting contacts. The characteristics 
react sensitively to an external magnetic field which, however, must now 
be applied perpendicular to the layer. The component is then referred to 
as a double-base magnetiodiode. 
An arrangement corresponding to the invention composed of two "short" 
sub-diodes can be understood and operated as a bipolar lateral transistor 
whose base terminal is divided in two. 
An arrangement corresponding to the invention comprising a field effect 
electrode similar to the structure shown in FIG. 4 can be considered and 
operated as a pair of complementary field effect transistors having a 
common gate. If one transistor is opened by a field effect, the other 
becomes blocked and vice versa. 
An arrangement corresponding to the invention with a field effect 
electrode, poled in the reverse direction as a diode, permits a field 
effect control of the reverse current. 
The many operating possibilities of the structure corresponding to the 
invention render the latter suitable e.g. as a test structure, for example 
for a quality check on SOS wafers. 
Although various minor modifications may be suggested by those versed in 
the art, it should be understood that I wish to embody within the scope of 
the patent warranted hereon, all such embodiments as reasonably and 
properly come within the scope of my contribution to the art.