Optical Properties of Cubic GaN Quantum Dots Grown by Molecular Beam Epitaxy

Abstract

We have investigated the optical properties of self‐assembled cubic GaN quantum dots (QDs) in a cubic AlN matrix grown in Stranski–Krastanov growth mode. Two different sample series are fabricated and optically characterized by photoluminescence measurements. Additionally, the experimental results are compared to theoretical calculations. Sample series A consists of one single QD layer with varying GaN amount. A red shift of emission energy of 140 meV is observed with increasing GaN deposition time. Simulations verify this behavior and can be explained by a decrease of the QD height. Sample series B has two layers of QDs on top of each other with different QD deposition amounts of three and six monolayers, respectively. The spacer layer thickness between the QD layers is 2 and 20 nm. A decreased emission intensity of the smaller QDs is measured for QD layers with smaller spacer layer thickness. This observation is a first hint of an electronic coupling between the two QD layers with thin spacer layer thickness resulting in tunneling of carriers from the smaller QDs to the larger QDs. Theoretical calculations further show that a strain induced structural coupling induces a vertical alignment of the QDs.

Influence of the free-electron concentration on the optical properties of zincblende GaN up to 1×1020cm−3

“…The effects of BMS and BGR on E CV as a function of the free-carrier concentration are described by Eqs. (15) and (19) using an averaged hole mass as given in Eq. (20).…”

“…On the other hand, several breakthroughs concerning the control and quality of zincblende GaN [6][7][8] were reported very recently. For certain applications, like quantum-dotbased functionalities [2,[9][10][11][12][13][14][15][16][17][18][19], a replacement of wurtzite by cubic nitrides seems possible in the near future. However, the band structure of zincblende GaN remains scarcely researched, despite the fact that, compared to wurtzite GaN, it is simpler due to its higher symmetry [20].…”

Femtosecond pump-probe absorption edge spectroscopy of cubic GaN

“…The influence of many-body effects like band-filling and band gap renormalization on the absorption onset in semiconductors is widely known [30][31][32][33][34]. Understanding these effects is essential for technical applications [35,36]. For highly n-type doped materials the Fermi-energy is pushed high into the conduction band.…”

Photoluminescence Line‐Shape Analysis of Highly n‐Type Doped Zincblende GaN

“…Furthermore, due to the higher crystal symmetry, the band structure of zb‐GaN is much simpler than that of the wurtzite phase . Therefore, zb‐GaN has the potential to replace wurtzite GaN in certain specific application areas such as quantum dot and quantum well‐based devices …”

“…[6] Therefore, zb-GaN has the potential to replace wurtzite GaN in certain specific application areas such as quantum dot and quantum well-based devices. [2,[7][8][9][10][11][12][13][14][15][16][17] Very essential for possible applications is the understanding of the n-type doped material. To achieve free-carrier concentrations exceeding 10 20 cm À3 , germanium was recently introduced as a donor instead of the standard donor silicon.…”