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Hall Effect Experiment - with computer interface HEX 21C

Introduction
The resistivity measurements of semiconductors can not reveal whether one or two types of carriers are present; nor distinguish between them. However, this information can be obtained from Hall Coefficient measurements, which are also basic tools for the determination of carrier density and mobilities in conjuction with resistivity measurement.

Description

Hall Effect experiment consists of the following:
1. Hall Probe (Ge Crystal) n & p-type
2. Hall Effect Set-up, DHE-21C
3. Electromagnet, EMU-50V
4. Constant Current Power Supply, DPS-50C
5. Digital Gaussmeter, DGM-202C
6. Computer Interface, SES-CAMM2

Hall Probes

(a) Hall Probe (Ge Crystal)
Ge single crystal with four spring-type pressure contacts is mounte d on a sunmica-decorated bakelite strip. Four leads are provided for connections with measuring devices.
TECHNICAL DETAILS
Material: Ge single crystal n or p-type as desired
Resistivity: 8-10Ω.cm
Contacts: Spring type (solid silver)
Zero-field potential: <1mV (adjustable) Hall Voltage: 25-35mV/10mA/KG It is designed to give a clear idea to the students about Hall Probe and is recommended for class room experiment. A minor drawback of this probe is that it may require zero adjustment. Hall Effect Set-up, DHE-21C
DHE-21 is a high performance instrument of outstanding flexibility. The set-up consists of a digital millivoltmeter and a constant current power supply. The Hall voltage and probe current can be read on the same digital panel meter through a selector switch.The unit is made compataible with SES-CAMM interface unit, for computer control option.

(i) Digital Millivoltmeter
Intersil 31⁄2 digit single chip A/D Converter ICL 7107 have been used. It has high accuracy like, auto zero to less than 10μV, zero drift of less than 1μV/°C, input bias current of 10pA max. and roll over error of less than one count. Since the use of internal reference causes the degradation in performance due to internal heating, an external reference has been used. Digital voltmeter is much more convenient to use in Hall experiment, because the input voltage of either polarity can be measured.

SPECIFICATIONS
Range: 0-200mV (100μV minimum)
Accuracy: ±0.1% of reading ±1 digit

(ii) Constant Current Power Supply
This power supply, specially designed for Hall Probe, provides 100% protection against crystal burn-out
due to excessive current. The supply is a highly regulated and practically ripple free dc source.
SPECIFICATIONS
Current: 0-20mA
Resolution: 10μA
Accuracy: ±0.2% of the reading ±1 digit
Load regulation: 0.03% for 0 to full load
Line regulation: 0.05% for 10% variation

Computer Interface, SES-CAMM
An interface (SES-CAMM) enables the userto operate the hall effect setup through a computer. the interface is attached to any USB port and on activation a GUI shows the computer control, data storage and graph plotting of the experiment. Also included is the option for automatic computation of hall coefficient, carrier mobility and carrier density.

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