pn‐Heterojunction Diodes with n‐Type In₂O₃

Abstract

contact metals, diodes with rectifi cation suffi cient for material characterization were reported. [ 33 ] Nevertheless, rectifi cation has to be improved considerably to exploit In 2 O 3 within detectors or transistors. The realization of pn-heterodiodes is an alternative approach toward rectifying devices and was successful for the case of ZnO as n-type layer as mentioned above. As recently demonstrated, ZnCo 2 O 4 and NiO are especially interesting as p-type layer since they can be deposited at room temperature on the n-type oxide and offer very high rectifi cation up to ten orders of magnitude. [ 9 ] We report on the electric properties of p-ZnCo 2 O 4 /n-In 2 O 3 (ZCO/InO) and p-NiO/n-In 2 O 3 (NiO/InO) heterodiodes investigated at room temperature (RT) by current-voltage (IV), capacitance-voltage (CV) measurements and admittance spectroscopy. Additionally thermal admittance spectroscopy (TAS) was performed on a selected diode. Results and DiscussionA wide-angle X-ray diffraction pattern of a nominally undoped-In 2 O 3 thin fi lm is depicted in Figure 1 . On the (001)YSZ substrates, the In 2 O 3 thin fi lm grows expectedly in [001] direction. This is in-line with investigations of MBE-grown In 2 O 3 layers on (001)YSZ. [ 34 ] An infl uence of the In 2 O 3 :Mg surface layers on the XRD pattern was not observed. Atomic force microscopy showed that all samples are compact, without voids and without faceting. The surface morphology depicted in Figure 2 for a sample without In 2 O 3 :Mg surface layer is similar to that reported by Bierwagen et al. for a thin fi lm (labeled S7) grown by MBE under In-rich conditions at 650 °C (with nucleation layer grown at 600 °C). [ 35 ] For our PLD-grown thin fi lm of Figure 2 the root mean square roughness is about 4 nm and suffi ciently low for growth of pn-heterodiodes.The free electron concentration of our nominally undoped-In 2 O 3 thin fi lms was obtained from Hall effect measurements and is with 3 × 10 18 cm −3 rather high for creating diodes thereon. For such high doping, the extension of the space charge region is small and tunneling currents are likely contributing to current transport across the interface. A reduction of the doping density close to the surface should increase the space charge layer width making tunneling less likely. This should result in smaller leakage currents but may also increase the series resistance of the diodes. Sample series with compensated In 2 O 3 :Mg layers with thickness d of 0, 10, and 100 nm pn-Heterodiodes comprising the wide bandgap semiconducting oxide In 2 O 3 and amorphous p-conducting NiO or ZnCo 2 O 4 are realized. In 2 O 3 is grown at 600 °C and the amorphous p-type oxides at room temperature by pulsedlaser deposition. Highest rectifi cation of about four orders of magnitude is observed for structures with Mg-doped In 2 O 3 layers having lower carrier density than undoped layers. The p-ZnCo 2 O 4 /n-In 2 O 3 diodes do not show degradation at elevated temperatures of 150 °C, whereas the p-NiO/n-In 2 O 3 diodes degrade irreversi...

Recent Developments in p‐Type Oxide Semiconductor Materials and Devices

“…Since the first all‐oxide junction diode demonstrated by Kudo et al, an increasing number of studies have been reported, with very good results . In spite of the short research history on oxide‐based p–n junctions, excellent‐performance devices were reported on p‐type amorphous ZnO·Rh 2 O 3 and ZnCo 2 O 4 (ZCO) . For a ZCO‐based diode, a recent report showed a large forward current to reverse current ( I f / I r ) ratio of ca.…”

“…In 2010, Kim et al fabricated p‐type ZnCo 2 O 4 thin film and the related p–n‐junction diode by PLD with controllable electrical performance, showing a bandgap of 2.3 eV and a conductivity of 21 S cm −1 , while the carrier density could be tuned from 10 16 to 10 20 cm −3 by controlling the oxygen pressure . Recently, Grundmann and co‐workers demonstrated high‐performance amorphous p–n‐junction diodes and junction field‐effect transistors using p‐type spinel oxide ZnCo 2 O 4 deposited at room temperature, indicating the great potential of this material, despite its low hole mobility (<0.1 cm 2 V −1 s −1 ) …”

Electrical Properties of Vertical p‐NiO/n‐Ga2O3 and p‐ZnCo2O4/n‐Ga2O3 pn‐Heterodiodes

“…Besides high power applications, Ga 2 O 3 and its alloys are suited for solar‐blind photo detection, realized so far by Schottky barrier metal‐semiconductor‐metal structures . However, heterojunction diodes comprising group‐III sesquioxides were also reported in terms of NiO/Ga 2 O 3 , Cu 2 O/Ga 2 O 3 , NiO/In 2 O 3 , and ZnCo 2 O 4 /In 2 O 3 pn‐heterostructures . In case of NiO/Ga 2 O 3 , the p‐type layer was Li‐doped and grown by the sol‐gel method on (100) β ‐Ga 2 O 3 single crystals with a free electron concentration of 5 × 10 17 cm −3 .…”

Structural, optical, and electrical properties of unintentionally doped NiO layers grown on MgO by plasma-assisted molecular beam epitaxy

“…7 Secondly, as a p-type transparent semiconductor it is a very relevant material for oxide-based gas sensors 8,9 as well as for pn-diodes and other transparent oxide electronics. 1,10,11 Additionally, NiO can be used as a hole transport and electron blocking layer in organic solar cells. 12 NiO films have already been grown by many methods, including sputtering, [13][14][15] metal evaporation with oxygen or nitrogen dioxide inlet, 16 pulsed laser deposition (PLD), 3,17 sol-gel coating, 18 or plasma-assisted molecular beam epitaxy (PA-MBE).…”