Visible Electroluminescence from Al-Porous Silicon Reverse Bias Diodes Formed on the Base of Degenerate N-Type Silicon
- PDF / 400,426 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 89 Downloads / 180 Views
Visible electroluminescence (EL) of porous silicon (PS) in solid state structures [1-8] has
recently excited a widespread interest in this material for potential applications in silicon technology.
Many of the previously described light emitting devices were characterized by a low time
stability, and a weak intensity of light emission. Moreover, the EL intensity was lower with respect
to the photoluminescence (PL) intensity from the same materials for many of the reported devices [9,10]. The EL was mainly observed under forward bias, except for [11,12]. In [11] EL was observed under a reverse bias of about 200 V. However, the light emission was quite unstable, with some tens of minutes of time duration. In this paper a technological process for obtaining light emitting Schottky junctions on the base of PS and aluminum is presented, showing high stability of emission. EXPERIMENTAL
The technological process followed here and the device structure are shown in Fig. 1. n-type single crystal silicon wafers with a resistivity of 4.5 Qcm were used as substrates in our experiments. A highly doped n' silicon layer of about 1 ttm thickness was formed on both sides of wafer by diffusion of phosphorous from the gas phase at a temperature of 950 'C for 40 minutes (Fig. la). After doping treatment the surface resistivity of the n' layer was 10 i2/square, (1020 dopant atoms/cm 3). Then the wafers were etched in hydrofluoridric acid in order to remove the oxide layer formed during thermal treatment. 659 Mat. Res. Soc. Symp. Proc. Vol. 358 01995 Materials Research Society
The PS layer was formed by anodization in transition regime, in 1% HF aqueous solution at 2-5 mA/cm 2 , as described elsewhere [13,14]. The thickness of the PS film was greater than the n+ layer, and a thin layer of the n-type substrate became anodized (Fig. lb). After anodization PL spectra were measured under UV laser excitation at 337 nm wavelength. To obtain a metallic contact, 0.5 tim thick aluminum was deposited by magnetron sputtering onto the porous layer (Fig. lc). The Al electrodes (pads) were obtained by standard photolithography and a subsequent electrochemical anodization process on aluminum, as described elsewhere [15]. Aluminum anodization produced the transparent insulating alumina (A1203) areas between the aluminum pads so that light could be transmitted (Fig. ld). The electrical contact on the wafer back side (not shown in the pictures) was provided by the n+ diffused layer. Devices were biased connecting either two adjacent pads on the upper layer or one of the pads and the back side contact. EL spectra were measured with the computer-aided spectrophotometer equipped with a cooled photomultiplier PEM- 100.
n+
a)
n +Porous Silicon nnSilicon Porous Silicon
-- 'Ti
b)
n
I'o Aluminum n+ Porous Silicon n Imrous Silicon n i icon
c) Light emission I
,,.1
U)
M
nn +Porous ,iroeuns Silicon Silicon
[
~ A120
Al
3
Fig. 1. Schematic view of the technological process: (a) n-type silicon wafer with n+
diffused layer; (b) after anodization
Data Loading...
