Tailoring Strain Engineering in Semiconductor Devices
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Leibniz MMS Days 202415 / 17
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Transcript: English(auto-generated)
00:05
My name is Costanza and as you can see from this slide, I come from IHP and IHP is a Leibniz Institute for microelectronics And these I am saying these because I am kind of an outsider every year in this conference
00:25
Because my main activity is to try to match the experimental results with my theoretical model And I am mainly working with people that are doing experiments having a close look To what is the future of technology?
00:41
so Instead of putting an abstract I decided to do the experiment of a graphical abstract What are the requirements of? Technology nowadays or especially in our field We want to focus on the idea of exploiting the potentiality of light
01:00
So going in the direction of optoelectronics But for lasing activities and for photo detectors and also the idea of working in The exploitation of the potentiality of material science for quantum technologies So mainly I will go in these two directions today
01:21
so the Title of the talk is tailoring strain engineering in CMOS microelectronics. The first part is strain engineering for optoelectronic devices and Even if we are in the area of silicon photonics, that is this wide branch of physics and engineering that wants to exploit the potentiality of light for
01:46
optoelectronics and for electronic devices we have a particular eye on germanium and the reason is that germanium is completely CMOS compatible and It has an almost direct it is an almost direct band gap material and
02:04
Also, there is a huge possibility of modify the band gap How do we work with respect to the band gap on one hand there is the strategy of introducing elastic strain So mechanical deformation that has pros and cons
02:24
So on one end we can lower and to modify the minima of both the conduction and The valence band in the case of germanium the conduction bands are pretty close to each other so the distance between the two minima is very small and
02:44
By applying a certain amount of strain we can really reach a level where the band gap becomes direct And also the mechanical deformation can modify the valence band So removing completely the degeneracy between heavy oil and the light oil band
03:02
however the scientific community has been talking about the potentiality of strain engineering in pure germanium for two decades nowadays and there are a lot of technological limitations related to the introduction of strain and So the presence of only germanium is really not enough
03:24
To gain a direct band gap material or to go into the direction of an only germanium based CMOS compatible laser So the next step is the introduction of alloy so germanium tin and germanium tin itself as the possibility of
03:45
Adjusting the conduction band minima, so allowing germanium tin to be a direct band gap material However, we have to leverage between these two contributions so on one end elastic strain on one hand on the other hand the introduction of tin and
04:03
The pros of the case of tin is that it's true that the high tin content can be achieved But on the other hand there is the presence of several defects or an harmonic effects and so on So what is the idea here of what I am trying to build up?
04:25
is a kind of a simulation platform that is able to provide a complete description of mechanical and optical properties of germanium or germanium tin devices With a modeling approach that for this reason
04:42
considers strain temperature alloy composition and the entire band gap landscape In the rest of the presentation I will show you an example and the example is of a germanium tin microdisc Built on a germanium substrate and we will see these a little bit more in detail after
05:05
On the other end the second pillar of the presentation is to try to understand what are the potentiality of material science and strain engineering in material science for quantum computing so
05:21
the first question that we have to reply to is why do we care about tin film material properties in quantum devices and The reply is that they can affect the band structure the transport properties the charge noise and whatsoever and
05:40
also Because they can really vary a lot along a simple surface So our technological facilities are not really allowing a complete uniformity So we need a real complete 3d description What do we? Mention when we talk about material properties we mention layer thickness
06:05
interface roughness lattice tray alloy composition defect density and distribution but As I mentioned already to you before my work is
06:22
To try to match modeling results with the experimental results that are produced in HP So let me show you what are the example of experimental set up that we are trying to match? Epsilon stands for strain. That is the minimum common denominator of this presentation
06:41
and so we can have for example Raman spectroscopy and XRD spectroscopy that are two different Techniques that allow to provide the strain landscape on a different level in the case of Raman We limit ourself to surface description in the case of XRD
07:01
We can have a much deeper and complete description of all the strain tensor What do I do and at this point I know that you may kill me I I mainly do simulation activities and for now I am working with commercial softwares and
07:21
What is the role of commercial software? So? Basically what is behind my calculation apart from a finite element meet element metered calculations that reproduce the geometries that are produced in HP I
07:40
Solved the hook slope. So from the interaction between the stress and strain So I have a stress tensor That is in most of the cases my input parameter I linked through the stiffness tensor and I can provide the map of a strain tensor
08:00
this is an example of a 3d description of a strain tensor, but Let me show For example a first comparison between Raman experiment and simulations Look at this picture. We are talking about Microdisc that I was describing to you before and
08:24
In the picture on the left we can see the Squares that are experimental results and the continuous line that are the computed Results what is interesting? Is that okay?
08:41
There is a good match But it is not at all a force the result in the sense that What we are really able to know from an experimental perspective is What are the deposition parameters of a germanium team films? This is something that is clear and can be understood on a microscopic level
09:03
This represents my input parameter and then the entire etching process And so the way the micro disk is relaxed is obtained by simulation part And on the other hand here you can also see that there is a good agreement with the displacement
09:21
another thing is that Most of the devices I am talking about are Designed to work not only at room temperature, but also at cryogenic temperature so we need to invest a little bit of effort in terms of
09:41
Understanding strain as a function of temperature and also here the model is not extremely complicated Leveraging on the difference between the coefficient of thermal expansion For example of the standard germanium grown on silicon We can understand the mismatch between the silicon and germanium thermal expansion coefficient that gives rise to
10:05
The thermal strain and so we can observe and also compare with experimental results Raman spectra that are obtained at different temperature. This is for Raman So Raman is representing actually a picture of
10:23
the strain profile Very close to the surface What is happening a little bit below the surface? This is something that we can calibrate we console and so tell Experimentally, but we can also tell theoretically for example by means of XRD spectroscopy
10:43
What I want to show is just for example these graphical representation of XRD map and the console map and in both of the cases you can see a ring that is an inside ring that is corresponding to the pillar to the substrate of germanium and
11:05
At least morphologically you can completely have a match between the two of them Even more actually interesting from my perspective was that all the time that I was doing Mechanical simulations I was assuming stuff like conservation of volume
11:24
And so there was a very funny game that was turning out with respect to yeah, we did with respect to the Diagonal components and so in this case you can definitely observe that my
11:41
Theoretical results are matching the experimental one Well In by means of photoluminescence experiment I could understand the behavior also of germanium of the presence of tin So the presence of tin is modifying the gap and shifting the peak to lower energies
12:04
so after having modified and after having observed the presence of different peaks at different positions of the micro disk We could give a complete description of the entire micro disk
12:21
So in this way making a parameterization of the gap We could see that the strain dependent band edge has a variation of around 220 milli electron volt between the center and the rim and That there is a specific area of around 40 milli electron volt that for example
12:45
In a range of in the temperature of 200 K represent a strong variation between both and top top and bottom in the rim area and Also that the role of the strain is completely compatible and comparable
13:02
With the one of tin I have unfortunately to leave to the F-arter discussion later the role of strain engineering in electron shuttling with titanium nitride and so with what is the next challenge of the quantum
13:22
Technologies in terms of quantum bus devices, but I can also tell that over there We could map both theoretically and experimentally all the strain components and actually offer an overview of the strain that there was first calibrated at room temperature and then
13:42
extrapolated at cryogenic temperature for the working device the quantum working devices and So what is the future the design of optoelectronic devices and the optimization of optoelectronic devices? And also the design of quantum devices
14:02
Before I conclude I want to also advertise this special issue of strain engineering in semiconductor materials where both Patricia and I are guest editors and Thank you for your attention