Investigation of III-V magnetic semiconductor thin films and heterojunction devices

Magnetic field control of semiconductor device properties is of great interest for novel electronics because it offers a way to control the spin degree of freedom of charge carriers. One way to achieve this control is the use of dilute magnetic semiconductor as an active element in semiconductor devices. In this work, the relationship between the magnetic and electronic properties of magnetic bipolar heterojunction devices is examined. InMnAs/n-type heterojunctions were fabricated using metalorganic vapor phase epitaxy. The capacitace of these devices was measured at room temperature as a function of magnetic field. The capacitance of these junction increases with magnetic field by up to 1.25% at 0.5 T. The change in capacitance suggests that there is spin splitting in the material. The magnetotransport properties of InMnAs/InAs heterojunction diode were measured as a function of magnetic field from 0 to 18 T and at various temperatures. These devices exhibit excellent rectifying properties at room temperature and zero magnetic field. When a magnetic field is applied, the junctions show resistive behavior, which dominates at high magnetic fields. The magnetoresistance of these diodes was measured as a function of current. The magnetoresistance for 15 mA through the device is 2600% at 18 T. The magnetoresistance of this device is attributed to efficient spin-polarized carrier transport. The conductance behavior of InMnAs diodes in high magnetic fields is analyzed to explain the spin selective transport. The change in current through the device at a constant voltage increases linearly with magnetic field for low magnetic fields and saturates at high magnetic field. The measured field dependence of the current change is attributed to the existence of a paramagnetic component, which determines the degree of spin polarization of the junction current. This work indicates that highly spin-polarized magnetic semiconductor heterojunction devices that operate at room temperature can be realized.;The first bipolar magnetic junction transistor was demonstrated. For an InMnAs p-n-p transistor structure, a dependence of amplification on magnetic field is observed at room temperature. The observed magnetoamplification is attributed to the positive magnetoresistance of the magnetic InMnAs heterojunction. The magnetic field dependence of the transistor characteristics confirm that the magnetoamplification results from the junction magnetoresistance. To describe the experimentally observed transistor characteristics, we propose a modified Ebers-Moll model that includes a giant positive magnetoresistance attributed to spin-selective conduction. The capability of magnetic field control of the amplification in an all-semiconductor transistor at room temperature potentially enables the creation of new computer logic architecture, where the spin of the carriers is utilized.