Neutron Transmutation Doping Conceptual Design Dr. Mosa Othman Silicon doping facility manger Egyptian Second Research Raector (ETRR-2) Atomic Energy Authority

Charge Carrier in Semiconductors At zero Kelvin temperature semiconductors behave as insulators. At zero Kelvin temperature semiconductors behave as insulators. at higher temperatures some of the electrons from the top of completely filled valence band (outer shell) can make a transition across the energy gap and occupy state in the bottom of the conduction As a result, electrons and holes are created. at higher temperatures some of the electrons from the top of completely filled valence band (outer shell) can make a transition across the energy gap and occupy state in the bottom of the conduction As a result, electrons and holes are created. These electrons and holes are referred to as charge carriers.

Intrinsic silicon conduction

Intrinsic Semiconductors A semiconductor whose electrical conductivity dominated by the thermally generated EHPs is called intrinsic semiconductor (undoped semiconductors). n = p = ni n = p = ni gi = ri gi = ri Both rates are temperature dependent. Conduction by holes differs from conduction by electrons.

Extrinsic Semiconductors: Charge carriers can be introduced in semiconductors by introducing impurities into the lattice. This method termed doping (addition of controlled amount of impurities into the semiconductor lattice). Impurities are called dopants. Dopants are either extra electrons (donors) or extra holes (acceptors). Impurities are called dopants. Dopants are either extra electrons (donors) or extra holes (acceptors). If the excess carriers are electrons, the doped semiconductor is called negative type (n-type). Conversely, if the excess carriers are holes the doped semiconductor is called positive type (p-type). If the excess carriers are electrons, the doped semiconductor is called negative type (n-type). Conversely, if the excess carriers are holes the doped semiconductor is called positive type (p-type).

N-type and p-type

Mobility: the mobility of hole is only about the half of the mobility of electron. The mobility is the velocity per unit applied electric field. mobility measures the ease of carrier motion through a semiconductor.

General requirements for NTD Temperature of silicon ingot during irradiation < 180 C Less than 100 C the diffusion of the impurities and defects are minimum

NTD utilization power devices, - high-class devices - standard devices. discrete device The basic advantages of NTD silicon in comparison with conventionally doped material, is the better distribution of phosphorus in the crystal.

Irradiation Rigs

Horizontal rig

main reactors used in silicon doping

Radiation Damage in Silicon simple point defects to large disordered regions, such as rod-like defects (10mm long and 200 A0 diameter). The fast neutron the head-on collision of a 1 MeV neutron with the silicon atom will knock out about 200 silicon atoms from their lattice sites The fast neutron the head-on collision of a 1 MeV neutron with the silicon atom will knock out about 200 silicon atoms from their lattice sites Concentration of these defects varies depending on the fast neutron flux to thermal ratio and Ingot temperature during irradiation. semiconductor parameters such as mobility, resistivity, and minority carrier lifetime are severely degraded.

Isothermal Annealing of Silicon Previous experiments have demonstrated that annealing for 30 minute at 750 0C is sufficient to obtain the anticipated carrier concentration and mobility in NTD float zone silicon (FZ) over wide range of neutron flounce

Quality of Doped Silicon Large Diameter For 6 inches (152 mm) diameter ingots that are irradiated in a light water moderated research reactor, the radial resistivity gradient (RRG) is too large even when they rotated through the irradiation process. The 6 inches ingots, which currently make up more than 10 % of the market, are only irradiated in heavy water moderated reactors or those that can provide a similar neutron spectrum for irradiating silicon. The 6 inches ingots, which currently make up more than 10 % of the market, are only irradiated in heavy water moderated reactors or those that can provide a similar neutron spectrum for irradiating silicon.

Power devices switching time

Resistivity Ranges for Electrical Components

Neutron transmutation doping facility design

Rig design

Neutronic design

Thermal design

New design old design

Axial thermal neutron flux profile in position (1)

Axial thermal neutron flux profile in position (2)

Irradiation method (1)

Method (2)

spacer design results

Radial resistivity measurement

Maximum percentage variation

Resistivity measurements

Axial resistivity variation due to neutron flux shape

Results of New Design Verification:

Axial Resistivity Variation

Radial resistivity variation

silicon ingot thermal characterization during irradiation

T max. 500mm, 6 ”

Max. energy rate 500mm, 6 ”

Temperature gradient in 500 mm ingot and 6 inches diameter Temperature gradient in 500 mm ingot and 6 inches diameter

Maximum temperature in the silicon, water gap and aluminum container

temperature calculation in 400mm ingot length and 6 inches diameter

Maximum temperature in 400 mm ingot and 6 inches diameter

Maximum energy rate in 400 mm ingot

temperature calculation for 250 mm ingot length and 6 ” diameter

Maximum energy rate in 250 mm ingot and 6 ” diameter

Temperature gradient in 250 mm ingot length and 6 ” diameter

Calculation of temperature in five inches ingot (new design)

Max. temp. 280mm and 5 inches

400 mm and 5 inches

Max. temp. and energy

500 mm ingot – 5 inches

Temperature distribution using (FEHT)

MEASUREDE TEMP.

CALCULATED TEPM. (FEHT)

Minority carrier life time samples

minority carrier life time samples

Old design minority carrier life time 7.66 micro-sec (270 minute annealing)

Old design minority carrier life time 4.66 micro-sec (270 minute annealing)

New design minority carrier life time 138 micro-sec (60 minute annealing)

Resistivity measuring in-line 4-point probe

Measuring minority carrier life time

Container fabrication and handling tools modification

Handling tool modification

New container