202
9 Semiconductor Spintronics
9.2 Issues to Be Considered
Integrating semiconductor and magnetism is essential since it may offer novel opportunities for utilizing spin degrees of freedom in semiconductor devices. The charge of
electrons and holes are exploited in the present-day electronic and photonic devices
for information processing or light emission (De Cesari et al. 2017; Frougier 2014;
Hirohataa et al. 2020; Bortolotti 2020; Hirohata and Takanashi 2014; Van Roy et al.
2004; S´anchez et al. 2007). The comparatively novel field of semiconductor spintronics looks for utilizing the spin of charge carriers to make transistors, light emitting diodes and lasers. The usefulness of such devices will depend on the availability
of materials having capability to manipulate or control of spin injection, transport
and detection well-matched with accessible semiconductor materials. Two important aspects are to be taken into account for the selection of materials towards the
realization of semiconductor spintronic devices. The first aspect is the retention of
ferromagnetism at and above room temperature, i.e., greater than 300 K. The second
aspect is the availability of already existing technology base for the desired materials
in another use.
Development of practical semiconductor spintronic devices relies on the fulfilment
of some vital and important requirements. They are as follows
(i) Efficient electrical injection of spin-polarized carriers,
(ii) High transmission efficiency of carriers within the host semiconductor or
conducting oxide,
(iii) The capacity of detection or collection of the spin-polarized carriers,
(iv) Controlling or manipulation of the spin transport by external agency like as
biasing of a gate contact on a transistor structure.
Extensive research on semiconducting materials shows that the bulk and thin film
semiconductors exhibit long spin lifetime and spin diffusion length. This is due to
their easy tuning of doping profile. The spin lifetime varies from tens of picoseconds
to several nanoseconds, whereas the spin diffusion length is usually hundreds of
nanometers. But several readings show that the spin lifetime and spin diffusion length
are larger in semiconductor nanowires compared to their bulk/thin film counterparts.
Theoretical studies reveal that the spin relaxation can be considerably concealed in
quasi-one-dimensional (1-D) nanostructures. This opens up a significant attention to
learn the electrical spin injection and transport in nanostructures.
Demonstration of several spintronic devices depends on successful spin injection
into semiconductors. Achieving efficient electrical spin injection is much easier in
ordinary metals and can be done through metallic spin valve structures. However,
this process is much more complex in case of semiconductors and is governed by
numerous factors:
(1) Conductivity mismatch: spin injection efficiency is very small due to the huge
difference in conductivity between ordinary ferromagnetic metals (FM) and
semiconductors (SC).
9 Semiconductor Spintronics
9.2 Issues to Be Considered
Integrating semiconductor and magnetism is essential since it may offer novel opportunities for utilizing spin degrees of freedom in semiconductor devices. The charge of
electrons and holes are exploited in the present-day electronic and photonic devices
for information processing or light emission (De Cesari et al. 2017; Frougier 2014;
Hirohataa et al. 2020; Bortolotti 2020; Hirohata and Takanashi 2014; Van Roy et al.
2004; S´anchez et al. 2007). The comparatively novel field of semiconductor spintronics looks for utilizing the spin of charge carriers to make transistors, light emitting diodes and lasers. The usefulness of such devices will depend on the availability
of materials having capability to manipulate or control of spin injection, transport
and detection well-matched with accessible semiconductor materials. Two important aspects are to be taken into account for the selection of materials towards the
realization of semiconductor spintronic devices. The first aspect is the retention of
ferromagnetism at and above room temperature, i.e., greater than 300 K. The second
aspect is the availability of already existing technology base for the desired materials
in another use.
Development of practical semiconductor spintronic devices relies on the fulfilment
of some vital and important requirements. They are as follows
(i) Efficient electrical injection of spin-polarized carriers,
(ii) High transmission efficiency of carriers within the host semiconductor or
conducting oxide,
(iii) The capacity of detection or collection of the spin-polarized carriers,
(iv) Controlling or manipulation of the spin transport by external agency like as
biasing of a gate contact on a transistor structure.
Extensive research on semiconducting materials shows that the bulk and thin film
semiconductors exhibit long spin lifetime and spin diffusion length. This is due to
their easy tuning of doping profile. The spin lifetime varies from tens of picoseconds
to several nanoseconds, whereas the spin diffusion length is usually hundreds of
nanometers. But several readings show that the spin lifetime and spin diffusion length
are larger in semiconductor nanowires compared to their bulk/thin film counterparts.
Theoretical studies reveal that the spin relaxation can be considerably concealed in
quasi-one-dimensional (1-D) nanostructures. This opens up a significant attention to
learn the electrical spin injection and transport in nanostructures.
Demonstration of several spintronic devices depends on successful spin injection
into semiconductors. Achieving efficient electrical spin injection is much easier in
ordinary metals and can be done through metallic spin valve structures. However,
this process is much more complex in case of semiconductors and is governed by
numerous factors:
(1) Conductivity mismatch: spin injection efficiency is very small due to the huge
difference in conductivity between ordinary ferromagnetic metals (FM) and
semiconductors (SC).