ezHEMS Hakkında Genel Bakış
Tasarım
NMI-ezHEMS cihazları, numunelerin elektronik özelliklerini ölçmek ve analiz etmek için tasarlanmış entegre bir donanım ve yazılım sistemine sahiptir.
Aynı zamanda NMI-ezHEMS cihazları, Dünya çapında birçok alanda kullanılan HEMS (Hall Etkisi Ölçüm Sistemleri) cihazları ile aynı prensipte çalışan ancak taşınabilirlik açısından daha portatif bir tasarıma sahip olma özelligine sahiptir.
Seçenekler
Sistem tasarımı sayesinde, sabit mıknatısa sahip iki farklı manyetik alan şiddet seçenegi mevcuttur.
Tasarım, standart sistemde 0.6T veya 1T manyetik alan şiddet seçenegi sunar.
Sistemde ayrıca farklı sıcaklık aralıklarında ölçüm yapılmasını sağlayan 3 farklı ölçüm başlığı bulunur.
Sistem, 80K ve 800K sıcaklıklar arasında “Düşük sıcaklık ölçüm başlığı-LT”, “Yüksek Sıcaklık Ölçüm Başlığı-HT” ve “Oda Sıcaklığı Başlık-RT” seçeneklerini içerir.
Düşük sıcaklık ölçüm kafasının tasarımı, sıvı nitrojen (LN2 / kriyojen içermeyen sistem) kullanılarak soğutma işleminin daha düşük bir maliyetle yapılmasını sağlar.
Aynı zamanda standart sistem tasarımı, LT ve HT ölçüm başlıkları içinde bulunan 3 boyutlu hareketli prob sistemi sayesinde numuneleri kolayca sistem için montajlama kolaylığını sisteme kolayca yerleştirilebilme olanağı sağlar. Özel talepler doğrultusunda bu özellik RT ölçüm başlıkları için entegre edilebilmektedir.
ezHEMS FAQ
QUESTION (S) : What is the difference between HEMS and ezHEMS devices?
ANSWER: There is no difference in the working principle in our HEMS and ezHEMS devices. The HEMS device covers the low, medium and high resistance range, while the ezHEMS device is considered the medium resistance measuring device. While using the electromagnet system in the HEMS device, the permanent magnet system is used in the ezHEMS device and there are only two different magnetic field options. In addition, the HEMS device is very large, the ezHEMS device is more portable and desktop size.
QUESTION (S) : What is the Hall Effect Measurement System (ezHEMS)?
ANSWER: A more portable and smaller version of the HEMS system designed based on the Hall Effect theory. The range of technical specifications is narrower compared to the HEMS device.
QUESTION (S) : What types of samples can we use for ezHEMS device?
ANSWER: Hall Effect measurements are indispensable in characterizing the properties of a wide variety of semiconductors and multi-layer devices, highly doped semiconductors, as well as highly conducting organic and inorganic materials with low sample resistance. Materials include GaAs, InP, InAs, Si, Ge, SiGe, HgCdTe, GaN, SiC, AlN, metal oxides, organic conductors, etc.
QUESTION (S) : What is the sample size for ezHEMS?
ANSWER: The sample sizes are from 5mm x 5mm to 15mm x 15mm
QUESTION (S) : What is the measurement type for ezHEMS?
ANSWER: Measurement types are I-V, I-R, van der paur, Hall Bar (6 contact), Resistivity, Temperature-Resistance (T-R)
QUESTION (S) : What is the measurement temperature options for ezHEMS?
ANSWER: There are 3 different temperature measurement options and measuring heads for ezHEMS;
80K-300K: low-temperature measurement option
300K: room temperature measurement option
300K-800K: high-temperature measurement option
QUESTION (S-T) : What is the difference between 0.6Tesla and 1Tesla magnetic field?
ANSWER: This choice varies depending on the user’s workspace and sample.
Samples must be exposed to the optimum magnetic field to have the correct mobility value. To determine the optimum magnetic field value, the magneto-resistance measurement of the sample is taken (resistance change measurement versus magnetic field change). therefore, the magnetic field must be sweepable.
Magneto-resistance measurement option is available in our HEMS devices, whereas in our ezHEMS devices, fixed magnetic field values are offered as two options.
QUESTION (S) :The system used contains the HT measuring head. What happens if I choose the LT measuring head in the software?
ANSWER: If you are using the high-temperature head (HT head) in your measurements, you must select the “HT head” option when you first turn on the software. If you choose a different temperature head in the software for the measuring head, your measurement results will be incorrect. Because different files belonging to each measurement head option are processed in the software. In other words, if you are going to use the high-temperature head, you must select the same name as the software on the software page. And measurement is taken by setting the desired temperature is taken.
QUESTION (S) : If we use the ezHEMS-RT head, how we can set the room temperature?
ANSWER: When you select the RT-measuring head in the software, the temperature will be automatically adjusted to room temperature. You do not need to set the temperature externally. We do not use a temperature sensor on RT measuring heads.
QUESTION (S) : We can use the HT and LT heads at the same time?
ANSWER: HT meaning is “High-Temperature measuring head”, and LT meaning is “Low-Temperature measuring head”. Measurement heads are different for HT and LT. If you want to measure between 80K-300K, you need to use LT-head. If you want to measure between 300K-800K, you need to use HT-head. If you just want to take measurements at room temperature, it will be enough to use RT-head (if your system includes the LT-head or the HT-head, you can also use these heads for room temperature measurements). At the same time, the software-background data for each measurement head is defined differently in the same software. That is, you cannot use any “measuring head” at the same time for these reasons.
QUESTION (S) : How does the LT measuring head cool?
ANSWER: We do the cooling process via Liquid Nitrogen (LN2) (no cryogen-free).
QUESTION (S) : When should we use the vacuum pump?
ANSWER: You must use the vacuum pump for all temperature measurements you have made (for LT: 80K to 300K, and HT: 300K to 800K measurements). If you do not use the vacuum pump, the LT-measuring head will freeze due to the liquid nitrogen. Or the inside of the HT measuring head and the sample will burn. At the same time, desired temperature values cannot be obtained in both measuring heads.
QUESTION (T-S): What is the difference between the bulk carrier concentration and sheet carrier concentration in Hall measurements?
ANSWER: Bulk carrier concentration is the number of carriers per unit vol. where sheet carrier concentration is the number of carriers per unit square [ it depends on dimensions of the sample].
QUESTION (T) : How can I determine which metal contact is better for semiconductors in measuring the Hall effect?
ANSWER: A lot of metals create Schottky-barriers. Therefore it is mandatory to the characteristic of the metal-semiconductor contact. A linear relationship between current and voltage must be observed. The contacts must be point-shaped and located near the edge of the sample. Otherwise, a correction factor is to calculate – but this is not specific for semiconductors. It has generally taken into account for precise measurements. For semiconductors, Ohmic contact materials are related to that certain semiconductor. For example, Au is producing a good Ohmic contact on the n-type GaP while it does not for the p-type and so on for other semiconductors.
QUESTION (S) : What are the standard examples that can be used for ezHEMS systems?
ANSWER: Our Hall Effect measuring devices follow the ASTM-standard as the most up-to-date standard accepted worldwide. According to the ASTM standard, the most known sample that can be used for our HEMS / ezHEMS measuring instruments may be “High-mobility material such as lightly doped n-type gallium arsenite”.
QUESTION (S) : Why is the geometry of the sample used in the hall effect a rectangle?
ANSWER: Only rectangular sample shape is not used for Hall Affect measurement.
According to the Hall Effect theory, there are two different “sample shape methods”; van der Pauw and Hall Bar. With our HEMS / ezHEMS devices have the opportunity to take measurements with 4 different vdP and 1 Hall Bar sample shape method supported by the ASTM standard.
QUESTION (T) : During the Hall measurements, should the first four readings with the positive magnetic field be opposite in polarity to the next four readings with the negative magnetic field?
ANSWER: The expected results under the magnetic field in samples produced close to the ideal are “numerical values that support each other with 1% tolerance and have opposite polarity”.
However, this status varies from the sample to sample unless the specimen is ideal. According to the measurement results taken under a positive and negative magnetic field, interpretations are made about the carrier type of the sample. In some cases, while numerical values support each other, signs may appear the same. In this case, it gives an overview of the density and homogeneity of the sample.
QUESTION (T) : What is a Hall voltage?
ANSWER: Hall effect is the production of a voltage difference called the Hall voltage across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current.
QUESTION (T) (specific): What is the Hall voltage for intrinsic semiconductor?
ANSWER: Hall effect is the production of a voltage difference called the Hall voltage across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current.
We expect it to be Zero as the concentration of holes and electrons are the same in an intrinsic semiconductor. But, As hall effect depends on conductivity & since conductivity depends on mobility [the mobility of electrons is more than holes]. So here intrinsic semiconductors behave more like an n-type semiconductor. Due to similarity with n-type semiconductor intrinsic semiconductor shows negative hall voltage coefficient.
QUESTION (T) : Which shows stronger Hall effect: metallic conductors or semiconductors?
ANSWER: Conductivity is inversely proportional to Hall Voltage, and semiconductors have lesser conductivity than metals. So, semiconductors show high hall voltage as compared to metals. thereby showing stronger Hall effect.
QUESTION (T) : Is electron mobility and conductivity the same in Hall Effect measurements?
ANSWER: The key factor in the sensitivity of a Hall effect device is the electron mobility. This is a measure of how quickly an electron can move through the material when under the influence of an electric field, and therefore how much it is deflected by the magnetic field through the device. Conductivity is the product of electron mobility and electron density.
QUESTION (T) : Why does Hall voltage have opposite polarity in p-type semiconductors as opposed to n-type semiconductors?
ANSWER: Because in a Hall experiment two fields are acting on the particles and each of them pushes positive and negative particles in opposite directions. The net movement is negative-negative for electrons and positive-positive for holes resulting in both types of carriers piling up in the same direction. Because they are of opposite charge, they create opposite pointing Hall field (and Hall voltage).
Electrons move in the direction opposite to the electric field and get deflected counterclockwise (upward) by the magnetic field. Holes move in the direction following the electric field and get deflected clockwise (upward) by the magnetic field.