Two-dimensional electron gas in Zn polar ZnMgO∕ZnO heterostructures grown by radical source molecular beam epitaxy

Abstract

A two-dimensional electron gas was observed in Zn polar ZnMgO∕ZnO (ZnMgO on ZnO) heterostructures grown by radical source molecular beam epitaxy. The electron mobility of the ZnMgO∕ZnO heterostructures dramatically increased with increasing Mg composition and the electron mobility (μ∼250cm2∕Vs) at RT reached a value more than twice that of an undoped ZnO layer (μ∼100cm2∕Vs). The carrier concentration in turn reached values as high as ∼1×1013cm−2 and remained nearly constant regardless of Mg composition. Strong confinement of electrons at the ZnMgO∕ZnO interface was confirmed by C-V measurements with a concentration of over 4×1019cm−3. Temperature-dependent Hall measurements of ZnMgO∕ZnO heterostructures also exhibited properties associated with well defined heterostructures. The Hall mobility increased monotonically with decreasing temperature, reaching a value of 2750cm2∕Vs at 4K. Zn polar “ZnMgO on ZnO” structures are easy to adapt to a top-gate device. These results open new possibilities for high electron mobility transistors based upon ZnO-based materials.

ZnO: From basics towards applications

“…As a result, low-temperature mobilities up to 2700 cm 2 /V s have been reported in ZnO QW [54,55]. Such values allow observation of the (integer) quantum Hall effect in ZnO.…”

Polarization discontinuity induced two-dimensional electron gas at ZnO/Zn(Mg)O interfaces: A first-principles study

“…30,31 The presence of the 2DEG is normally confirmed by Hall effect and capacitance measurements. 24,27,28 The observation of the quantum Hall effect 25 and the fractional quantum Hall effect 29 in these heterostructures testifies to the high quality of these interfaces. Charge concentrations on the order of 10 13 cm −2…”

“…23 Recently, a different type of system supporting a 2DEG, wurtzite ZnO/Zn(Mg)O heterostructures, has been investigated experimentally. [24][25][26][27][28][29][30][31][32] These heterostructures are usually grown using molecular beam epitaxy; 24,25 however, a 2DEG was also demonstrated in samples grown with metal-organic vapor deposition which is suitable for mass production. 30,31 The presence of the 2DEG is normally confirmed by Hall effect and capacitance measurements.…”

Exciton confinement in homo- and heteroepitaxial ZnO/Zn1 − xMgxO quantum wells with x < 0.1

“…3 Several groups have investigated heteroepitaxial growth of ZnO/(ZnMg)O single heterostructures, [4][5][6] single quantum wells (SQWs), [7][8][9][10][11][12][13][14][15] double quantum wells, 16 and multiple quantum wells [17][18][19] on various substrates such as c-plane, a-plane, and r-plane sapphire, c-plane GaN/sapphire templates, Si(111), and ScAlMgO 4 . However, only very few results of homoepitaxial growth of polar ZnO/(ZnMg)O SQWs have been reported, 20 although this growth technique can lead to improved structural, optical, and electrical properties of the resulting ZnO films.…”