Spin-Dependent Transport in GaN Light Emitting Diodes
- PDF / 658,066 Bytes
- 10 Pages / 414.72 x 648 pts Page_size
- 118 Downloads / 220 Views
important is the difficulty to achieve stimulated emission from the group m-nitrides:
The extremely short lifetime of the luminescence requires enormous excitation densities to achieve the necessary occupation inversion. The short lifetime is most probably due to an unidentified deep defect leading to an efficient nonradiative recombination path quenching the radiative transition. The large bandgap of the material makes the simple extension of existing techniques for the electrical characterisation of defects in other semiconductors difficult. As an example, the thermal excitation used in conventional deep level transient spectroscopy (DLTS) has to be replaced by optical excitation, which has indeed led to the observation of several deep states [1]. Here, we will show that both donor and acceptor levels as well as deep defects can be detected via electronic transport measurements in GaN diodes with the help of electrically detected magnetic resonance (EDMR). We will briefly discuss why magnetic resonance can influence electronic transport processes such as recombination. Imagine that an electron encounters a paramagnetic defect state (ie. a singly occupied defect) on its path through the sample. Both have a spin of S=1/2. The possible recombination step would in this case be the capture of the electron by the defect leading to a doubly occupied defect. The Pauli principle only allows this final state to be an S=O singlet state. However, the spins of the two initial states can form both a singlet or a triplet (S=1). Since angular momentum is conserved in a non-radiative recombination, only the initial electron/defect states 657 Mat. Res. Soc. Symp. Proc. Vol. 395 01996 Materials Research Society
forming a spin singlet will be able to recombine, the transiton of the triplet is forbidden. However, flipping the spin of either the electron or the defect with the help of electron spin resonance (ESR) transfrom the triplet into a singlet state. This increases the total recombination rate. Although the induced resonant changes of the total current through the device are small (typically of the order of 10-6 at room temperature), they can easily be measured with the help of lock-in techniques. We then obtain the resonance signature of both states involved in the recombination which, in principle, allows us to form a detailed model of the transport processes present in the material or device.
Electron spin resonance (ESR) provides detailed information on the microscopic structure of paramagnetic states in semiconductors. In GaN, several groups have studied the ESR signature of the residual donor at low temperatures [2,3]. However, due to the low sensitivity of this method, comparatively thick samples have to be studied. Optically detected magnetic resonance (ODMR) uses similar selection rules for the resonant detection of paramagntic states involved in recombination processes as EDMR. Indeed, this method has been applied successfully to GaN, and additional resonances, assigned to a deep defect and the Mg acceptor-state,
Data Loading...
