Infrared Light Emitting Diodes Using Silicon Crystal
This chapter reviews the fabrication and operation of a Si-LED that emits infrared light. In contrast to the single-step spontaneous and stimulated emission processes described in Sect. 1.3.1 , those of infrared light emission are two-step processes (Sec
- PDF / 1,947,020 Bytes
- 14 Pages / 439.37 x 666.142 pts Page_size
- 104 Downloads / 211 Views
Infrared Light Emitting Diodes Using Silicon Crystal
This chapter reviews the fabrication and operation of a Si-LED that emits infrared light. In contrast to the single-step spontaneous and stimulated emission processes described in Sect. 1.3.1, those of infrared light emission are two-step processes (Sect. 1.3.2). This is because the emitted photon energy is lower than E g .
3.1 Device Fabrication As with the case described in Sect. 2.2, an n-type Si crystal with low As concentration was used [1]. By doping the crystal with B atoms, the Si crystal surface was transformed to p-type, forming a p–n homojunction. An ITO film and an Al film were deposited on opposite surfaces of the Si crystal for use as electrodes. A forward bias voltage of 16 V was applied to inject current (current density of 4.2 A/cm2 ) in order to generate Joule-heat for performing annealing, causing the B atom to be diffused and varying the spatial distribution of its concentration. During the annealing, the Si crystal was irradiated, through the ITO electrode, with laser light (light power density, 10 W/cm2 ) whose photon energy hvanneal was 0.95 eV (1.30 µm wavelength). Since hvanneal is lower than E g of Si, the radiated light is not absorbed by the Si crystal. Therefore, in the regions where DPPs are hardly generated, B diffuses simply due to the Joule-heat of the applied electrical energy. However, in the regions where DPPs are easily generated, the thermal diffusion rate of the B atom becomes smaller via the following processes: (1) Since the energy of the electrons driven by the forward-bias voltage (16 V) is higher than E g , the difference E Fc − E Fv between the quasi Fermi energies in the conduction band E Fc and the valence band E Fv is larger than E g . Therefore, the Benard–Duraffourg inversion condition is satisfied. Furthermore, since
© Springer International Publishing Switzerland 2016 M. Ohtsu, Silicon Light-Emitting Diodes and Lasers, Nano-Optics and Nanophotonics, DOI 10.1007/978-3-319-42014-1_3
29
30
3 Infrared Light Emitting Diodes Using Silicon Crystal
hνanneal < E g , this light propagates through the Si crystal without absorption and reaches the p–n homojunction. As a result, it generates DPPs efficiently at B atoms. Since stimulated emission takes place via DPPs (Sect. 1.3.2), the electrons generate photons by the stimulated emission and are de-excited from the conduction band to the valence band via the phonon energy level. (2) The annealing rate decreases because a part of the electrical energy for generating the Joule-heat is spent for the stimulated emission of photons. As a result, at the regions where the DPPs are easily generated, the B atoms become more difficult to change. (3) Spontaneous emission occurs more efficiently at the regions in which the DPPs are easily generated because the probability of spontaneous emission is proportional to that of stimulated emission. Furthermore, with temporal evolution of process (2), the light from stimulated and spontaneous emission spreads through the whole Si cryst
Data Loading...
