Schottky Diode Lab Report

Sc naughtytky Diode Lab ReportINTRODUCTION A Sc racytky diode is the common name for a surface-semiconductor unit junction, it is the work function between the semiconductor and metal that determines whether the junction is ohmic or rectifying 1. This lab bequeath focus on the fabrication of a Schottky diode and the characteristics they possess. In principle, Schottky diodes argon rectifying as the rate of f number one dirty dog notwithstanding flow one way. They flowerpot in like manner handle high frequencies and strike lower reason button which makes them ideal for m each applications 2. These include world extensively use in fountain electronics, general purpose rectifiers and collectable to its non-linear I-V curves, it is able to be use as a varistor which in troll throw out be employ for voltage suppression 2. Also at that place is a low capacitor of the device which makes it more ideal than alternative diodes.OVERVIEW OF THEORYAn Ohmic match is requested on the bottom part of the type as without this, whatever standards taken would create a very high resistance as the semiconductor and the metal probe utilise to measure would create both diodes facing each other, therefore no watercourse could flow. This is overcome by diffusing indium and germanium onto the semiconductor wafer. Gold is also utilize to prevent whatever oxidisation on the standard. The wafer is premierly placed into the pipage furnace with the gold, indium and germanium on it past heated at 420C for 90 stand bys. This is to enable quantum tunnelling so there is circumstantial resistance and only the semiconductor and top metal argon measu rubicund.Figure 1 shows the zippo band diagram of a metal-semiconductor junction, which is rectifying as the work function of semiconductor is higher than that of the metal.Figure two is the Schottky diode characteristics and when comp atomic number 18d to figure 3, the PN diode characteristics, it shows that the tur n on point is lower in the Schottky diode, which means less(prenominal) power is conducted to operate, however there is a higher leakage current in reverse bias. cheat FABRICATION When working with such good influenced devices, safety essential be upheld at every milestone. This is first oblige by the dress code that is required in the laboratory. Each psyche must wear an overcoat, safety ice rinkes, gloves, overshoes and a hair net. collectible to even the sm all in allest particles world able to affect each specimen, the dress code is unavoidable to ensure that very little dust gets into the clean fashion. Also, there atomic number 18 many different chemicals in the live therefore more precautions ar needed when working with them. All guidelines set out by the fake of Substances Hazardous to Health (COSHH) regulations must be vigorously followed. Using these guidelines, all chemicals must be used inside a fume press as any spillages result be contained and the fum es can be collected. There argon also hot plates and other specialised equipment that should be handled with compassionate to ensure no damage comes to either the user or the machine itself.The cleanroom is comprised of 3 different areas. The first is where the entrants of the cleanroom put the safety equipment on, the second is the principal(prenominal) laboratory area and the final is the yellow room. Each room is machine-accessible to the conterminous with interlocking doors that only open when all others are closed. This is because each has a different pressure level due to the need of having to keep as little dust in the main room to stop the contamination of stresss. The high pressure level in the main room help to filter out any unwanted particles in the room. The air flow is also monitored to ensure that if there is a slough in pressure, the right actions can be taken to rectify any issues. The yellow room has special lighting due to the sensitivity of the devices that leave be later described, however the main difference is that both red and blue colours have been taken out as the devices are easily affected by UV lights. The clean room being used for this experiment is classified as Class 6, this refers to the particle sizing compared to the maximum particle niggardness. at one time all safety aspects have been covered, the process to create the device can begin. The first step is cleaving. This is where the wafer is cut into down(p) sample sizes, usually 3x3mm, as the wafer is very expensive and only a small amounted is needed to wind up the experiment. A special machine can be used to perform this however it is also achievable by hand.When the sample has been cut to the indispensable size, it is essential that a iii map solvent cleaning method is used. This is to ensure that there is little to no dust on the sample. To recognise the three stages, the sample must first be placed into a beaker of N-Butyl Acetate (NBA) that has been heat ed on a hotplate. Once it has been in the beaker for a short amount of time it must be reassignd and then cleaned with a cotton swab that has also been dipped in the NBA. This is through with(p) by rolling the swab earlier whilst pulling back so that as many particles as assertable are collected. The sample is the turned 90 and swabbed again to collect any particles that may have been missed. This process is again completed but with the sample being dipped in Acetone and then Isopropyl Alcohol to complete the three stage cleaning. After this has breatheed, the sample is then dried-out with north gas.Due to the small size of the sample, it is much easier to handle on a larger material, such as a glass slide. This is done by heating the slide on a hot plate then melting wax onto it then placing the sample on that. This is then leave to cool and give now be ready for the adjacent stage.The bordering stage is photolithography. This is required to put a pattern onto the sample so that testing of the device can happen and is exclusively completed in the yellow room. As mentioned earlier, the stages throughout this part will mean that the sample will be affected by UV lights so it is necessary to complete this in the designated room. Firstly, the sample is placed on a hot plate for one minute. Then it is placed onto the spinner and spun at 4000rpm for 30 seconds and dried with nitrogen gas. Now a few drops of photoresist are added, this is the answer our sample will be printed with. Again the sample is placed in the spinner 30 seconds and then soft baked on a hot plate for exactly 1 minute. If the sample is baked for as well short, the sample will stick to the machine used in the next part and if baked for too long the sample may live damaged. Once the sample is completely dry, it is placed into the mask aligner. Each coigne is lined up using the microscope and the camera so that a complete pattern is crossways the sample. Once completed, the machine i s set for 6 seconds and exposes the sample to UV light, the time needed varies with different materials. The sample is then wash in a beaker of developer solution for exactly one minute as again if the time is not strictly adhered to, it can have unbecoming effects on the sample. Finally it is washed in deionised water and dried with nitrogen gas. Now the sample has the same pattern which was imprinted from the mask aligner as the photoresist has been taken away from the split that are needed.Now metallisation must happen as the sample needs a metal layer placed onto it. This is completed by placing the sample in a vacuum put up and placing a small amount of aluminium inside a due west coil. Tungsten is used as the process involves heating the domiciliate to a point where the aluminium will evaporate but the other materials will not. As the chamber heats, the aluminium creates a hack layer across all of the inside of the chamber, this layer is approximately 0.2m which can be calculated by knowing the amount of aluminium used. As the chamber is a vacuum, there will be no chance of an oxide layer being created which would ruin the sample. Using the vacuum also means that less pressure is needed and that a lower temperature can be used.Due to the evaporation covering the entire surface of the sample, the Lift-off process is needed to back away any separate of the metal that is not needed. The photoresist has protected some parts of the semiconductor from the metal and this needs to be removed to leave the parts where there is a direct contact between the metal and semiconductor. This is done by placing the sample in a beaker of acetone and syringing the sample until the photoresist, and the metal on it, is removed. This process is usually quite quick but can take anywhere up to 20 minutes.The final stage forward the sample is ready for experimental watching is to remove the sample from the glass slide. This is completed by heating the sample on a hot pl ate until the wax has melted. Once this happens the sample is then cleaned with the same three stage solvent cleaning method earlier describe to remove any remaining wax. Finally it should be dried with nitrogen gas, with care taken as the sample could be blown away due to it not being on the glass slide. Once the all stages have been completed the sample is ready for analysis at the probe station.DEVICE CHARACTERISATION Now the slide is ready, the first test can commence. The sample is placed in the probe station and a Source measurement unit (SMU) is connected to the probe station and a computer so the results can be recorded. As the SMU acts as both the source and meter, this is connected to one probe whilst the base is connected to the other. Now the probe is guardedly aligned onto one of the small circles that has been created on the sample, with great care being taken due to the sample only having a very thin layer which is easily penetrable. Next, a voltage sweep is created from -3V to 3V with a low current limit so ensure the device is not broken. Once the data has been recorded the probe is moved onto a different circle and the process is repeated.The behaviour of the Schottky diode can be modelled by the interest equationIf the gradient of the voltage versus Log(J) is taken, the equation can be rearranged to get hold n. n is the factor that is used to determine the non-ideality of the diode.The values for the current density and n can be found in table 1.The next experiment is to measure Capacitance verses Voltage. The measurements will be taken in a similar way to the IV measurements however, a LCR meter will be used instead. This is due to the LCR being able to measure electrical condenser and phase angle. For these measurements, the sweep will start at 0 and be reduced until the phase angle is roughly 75. This is due to the need of being in reverse bias.The following formula can be used to find the dopant density of the semiconductor.The dopan t density of the sample was found to be ***. The voltage barrier of each diode can be found by taking the gradient of the graphs.DISCUSSION AND CONCLUSIONSReviewing the IV graphs it is clear that as the current increases, the linearity of the current density starts to become unstable. This can be explained due to the possibility of defects in the sample. In most industry practices, technicians are not present during the manufacturing fabrication stage and is solely completed by machines. Even though great care has been taken to ensure that the samples used in this exercise have been unaffected by unwanted particles, there is clearly still evidence of impurities throughout the sample.When the data from the CV graphs is reviewed, the observation that as the diameter of each diode increases, the barriers height decreases can be do. Having a higher barrier height is important as this will create a rectifying contact which is beneficial as it only lets the current flow one way. Therefor e the conclusion can be made that having diodes with lower diameters have more advantages when creating Schottky diodes.This lab has demonstrated how a Schottky diode has been made and what the different characterises are. Great care has been taken to ensure little impurities affect the sample however there is still room for utility and shows the essential need to uphold the safety requirements. Due to the low power needed and the fast switching abilities Schottky diodes are able to be used much more universally than standard PN diodes.