Properties of Delta Doped Al 0.25 Ga 0.75 N and GaN Epitaxial Layers
- PDF / 58,918 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 223 Views
L11.44.1
Properties of Delta Doped Al0.25Ga0.75N and GaN Epitaxial Layers Jeffrey S. Flynn, Leah G. Wallace, Joe A. Dion, Edward L. Hutchins, Helder Antunes and George R. Brandes Advanced Technology Materials, Inc Danbury, CT 06810, U.S.A.
ABSTRACT
Delta doping (paused growth doping) was investigated as an alternative to uniformly distributing the dopant in the nitride semiconductor layer. In this work, delta doped layers were produced in MOVPE-grown AlGaN and GaN layers at a susceptor temperature of 1220°C by turning off the group III precursors (TMG and TMA) and introducing into the reactor a silicon precursor Si2H6 (disilane) for a fixed period (pause time) before growth was restarted. The compositional and electrical properties as a function of aluminum content and dopant flux were investigated for nitride layers on 2 inch c-plane sapphire substrates. Secondary ion mass spectroscopy (SIMS) measurements revealed a sharp silicon peak with a FWHM of 5.7 ± 0.6 nm for an Al0.25Ga0.75N sample and 10.0 ± 0.6 nm for a GaN sample with sheet charges of 7.9x1012 cm-2 and 9.9x1012cm-2, respectively. Room temperature Hall mobility as high as 265 cm2 V-1s-1 for a sheet charge 7.9x1012 cm-2 was demonstrated for delta doped Al0.25Ga0.75N layers, but the mobility enhancement saturated and then decreased with increasing sheet charge. Room temperature sheet charge increased with increasing dopant flux for delta-doped AlGaN and GaN layers. Sheet charge density as high as 2.2x1013 cm-2 and 1.3x1013 cm-2 was measured at room temperature for Al0.25Ga0.75N and GaN delta doped layers, respectively. Under identical doping conditions, the Hall sheet charge of the delta doped Al0.25Ga0.75N layer was approximately half as large as GaN layers. The impurity and electrical characteristics of the delta doped layers are further discussed.
INTRODUCTION
High quality delta doped structures have played an important role in conventional III-V semiconductors [1] and are well-known to reduce DX centers and the corresponding deleterious effects in AlGaAs [2], improve p-HEMT mobility, increase breakdown voltage [3,4] and provide improved temperature-stability in laser diodes [5,6]. Given these significant benefits to AlInGaAsP, it is surprising little systematic experimentation of delta doping has been done in III-nitrides. GaN delta doping was demonstrated with relatively narrow C-V profiles, a few nanometers in width, similar to GaAs [7,8]. Delta doped layers in AlGaN HEMT heterostructures were recently demonstrated exhibiting high peak transconductance of 240mS mm-1 [9] and high mobility of 12,000 cm2V-1s-1 at 77°K [10]. In this paper we report results of measurements made on samples of delta doped GaN and Al0.25Ga0.75N grown by low pressure,
L11.44.2
MOCVD. The differences between the samples are investigated via SIMS Si impurity profiling, 300°K and 77°K Hall sheet charge and mobility measurements.
EXPERIMENT
The nitride samples in this study were grown in an AIX 200 / 4 MOCVD reactor on (0001) sapphire substrates with a conventional low t
Data Loading...
