Fabrication and characterization of Mg₂Si pn-junction Photodiode with a ring electrode

Abstract

We have fabricated Mg2Si pn-junction photodiodes with an Au-ring electrode and a SiO2 passivation layer by means of a lift-off photolithography process. Current-voltage (I -V) characteristics of the photodiodes showed obvious rectifying behavior at room temperature. The ideality factor of n determined from the slope of I -V characteristics was 1.76 -1.92. The photodiode showed a photoresponse with threshold energy of approximately 0.6 eV under a zero-bias condition. The intensity of peak photoresponse was improved approximately three times compared with the opaque Au-circular electrode type Mg2Si photodiode previously reported.

Fabrication of Mg₂Si pn-junction photodiode with shallow mesa-structure and ring electrode

“…In the reverse bias, current density was increased as the ID becomes larger. This behavior indicates that the bulk leakage current would be dominant in the reverse biased leakage current [7,10]. Figure 3 (b) shows J-V characteristics of planar-type (ID = 200 μm) [7] and shallow mesa-type (ID = 400 μm) Mg2Si PDs with ring electrode.…”

“…This behavior indicates that the bulk leakage current would be dominant in the reverse biased leakage current [7,10]. Figure 3 (b) shows J-V characteristics of planar-type (ID = 200 μm) [7] and shallow mesa-type (ID = 400 μm) Mg2Si PDs with ring electrode. The reverse bias current density of shallow mesa-type PD was achieved about 0.18 A/cm 2 at -3 V, which is smaller than the planar-type one, even though the shallow mesa-type had larger ID.…”

“…Recently, we have reported Mg2Si pn-junction photodiodes (PD) fabricated by the thermal diffusion of Ag dopant into the n-type Mg2Si substrate and their clear photoresponse below 2 μm [5][6][7][8]. However, their sensitivity is needed to improve for practical device applications.…”

Growth of 2-inch diameter Mg₂Si crystal by the VGF method under Ar normal pressure

“…Magnesium half-silicide (Mg2Si) is an interesting semiconducting material suitable for mass production because its constituent elements are abundant in the earth's crust, inexpensive, and have low toxicity. Mg2Si p-n-junction photodiodes have attracted considerable attention as inexpensive optical detectors in the short-wavelength infrared region [1][2][3][4][5][6][7][8] because of their indirect bandgap energy (0.61 eV) at room temperature [1][2]. Bulk single crystals with low electron concentrations have been developed using the vertical Bridgman (VB) method [1,3], and the p-n junction was directly fabricated onto the n-type substrate by simple thermal diffusion [2,[4][5].…”

Observation of pn-junction depth in Mg₂Si diodes fabricated by short period thermal annealing

“…Previously, we reported the fabrication of Mg2Si pn-junction diode by diffusing Ag dopant into n-type Mg2Si substrate and its photoresponse below 2 µm [7]. The photosensitivity of the diode is improved by making the shallower pn-junction and the ring electrode in place of the opaque circular electrode [12,13]. However, those reported diodes had deep pn-junction more than 75 µm, because of the high thermal diffusion temperature (550 ℃) and the relatively long annealing time (4 min) compared with the high diffusivity of Ag in Mg2Si [11].…”