John Rennie

Room Temperature Pulsed Operation of Nitride Based Multi-Quantum-Well Laser Diodes with Cleaved Facets on Conventional C-Face Sapphire Substrates

We demonstrate room temperature pulsed operation of nitride based multi-quantum-well (MQW) laser diodes with cleaved mirror facets grown on a conventional C-face sapphire substrate. Cleavage was performed along the direction of the sapphire substrate, and the resultant facet was analyzed using an atomic force microscope (AFM) and theoretical calculation. A single peak emisson, at a wavelength of 417.5 nm, with a full width at half-maximum of 0.15 nm, was obtained. The threshold current density of the laser was 50 kA/cm2 and a voltage for the threshold current was 20 V.

High temperature (77 °C) operation of 634 nm InGaAlP multiquantum‐well laser diodes with tensile‐strained quantum wells

634 nm InGaAlP multiquantum‐well (MQW) laser diodes, with tensile‐strained InGaP well layers, have been investigated. A threshold current as low as 59 mA was achieved, at 20 °C, under continuous wave (cw) operation. These MQW laser diodes were able to operate up to temperatures as high as 77 °C under cw conditions. This maximum cw operation temperature is the highest ever reported for 634 nm laser diodes. These MQW laser diodes have shown stable cw operation over 2000 h at an output power of 3 mW, at an ambient temperature of 50 °C.

Effect of metal type on the contacts to n-type and p-type GaN

Abstract The electrical properties of various metal contacts to both n-type and p-type GaN were investigated to determine the underlying trend between the metallic contact workfunction and the resultant Schottky barrier height between the said contact and the GaN material. It is concluded that, contrary to the expected trend, Fermi level pinning is not only present but is quite strong, with the effect being greater in the p-type material. The S factor (the index of interface behaviour) was seen to be reduced from 1.00 to 0.21 and 0.01 for n and p-type GaN, respectively.

Measurement of the barrier height of a multiple quantum barrier (MQB)

A method of using a light-emitting diode structure with two active regions to measure the excess barrier height induced by the inclusion of a multiple quantum barrier structure is outlined. For a multiple quantum barrier structure previously used in a visible laser device, the resultant increase in barrier height was found to be 26 meV. The effect of the first barrier thickness on the produced barrier height is also investigated. It was found that by optimizing this parameter, the induced barrier height could be increased to 55 meV. These results are compared with those predicted by theory, and certain discrepancies between them are discussed. >

The analysis of contact resistivity between a p-type GaN layer and electrode in InGaN MQW laser diodes

Abstract The individual elements attributing to the excess voltage drop in the nitride-based laser diodes were investigated. The specific contact resistivity ρ c to p-type GaN was estimated by transmission line model (TLM) method and was estimated to slightly vary from 3.2×10 −3 to 6×10 −4 Ω cm 2 in the current range of 1–10 kA cm −2 . It is found that a low specific contact resistivity was obtained by optimizing both the acceptor density of p-type GaN and the contact metals. The respective voltage drop at the p-side contact in our laser diodes was found to be 5.6 V for a device with a threshold current density of 6.7 kA cm −2 (Ith=100 mA) at 14 V under pulsed current injection at room temperature. It is found that the excess voltage drop in these devices is mainly due to the p-side contact resistance.

Analysis of transverse modes of nitride-based laser diodes

The analysis of the perpendicular far field patterns of nitride-based laser diodes with various types of AlGaN cladding layers is demonstrated. Other results obtained with our nitride-based laser diodes are also demonstrated and discussed.

Vertical-cavity surface-emitting lasers constructed with AlQ3 active regions employing a DBR structure

The use of a Tris-(8-hydroxyquinoline) Aluminum (Alq3) organic active region within a distributed Bragg reflector (DBR) mirror-cavity structure is described. The resultant device showed a narrowing of spectral output with increasing DBR usage significantly purifying the broadband emission of Alq3. Higher excitation intensities resulted in the production of lasing with a threshold of 3.2 kW/cm2.

Schottky Barrier Height Reduction for p-ZnSe Contacts by Sulfur Treatment

We have demonstrated the relationship between the structural and electrical properties of the chemically treated p-type ZnSe surface. The unstable Se-rich ZnSe surface, formed by an acid etchant, is shown to be removed by sulfur treatment. The sulfur treatment has been found to have the effect of lowering the Schottky barrier height at the Au/p-type ZnSe interface. This barrier lowering has been found to be effective in reducing the operation voltage of the ZnSe-based devices.

Operation voltage reduction in ZnSe‐based light‐emitting diodes due to the use of n‐type AlGaAs and CdZnSe buffer regions

On proposing the existence of a significant barrier between n‐type GaAs and n‐type ZnSe, in ZnSe‐based devices, we examined various offset reduction buffers, in standard light‐emitting diode structures, to assess their ability to reduce the excess voltages applied across this interface during operation. The main buffers investigated were CdZnSe and AlGaAs. The AlGaAs buffer was seen to have the largest effect, reducing the operation voltage from 17 V (GaAs buffer only sample) to 6.5 V at a current density of 1 A/cm2. Our results clearly indicate the utility of such buffer regions in reducing the operation voltages of these devices.

Low voltage carrier injection in ZnSe-based blue-green laser diodes on p-type GaAs substrates with InGaAlP band offset reduction layers

Summary form only given. A low voltage current injection is demonstrated theoretically and experimentally for ZnSe/CdZnSe blue-green lasers. Insertion of InGaAlP layers reduce the excess voltage drop, due to the large valence band offset between the p-type GaAs substrate and p-type ZnSe layer. The InGaAlP layers are also useful as high concentration p-type ZnSe layers can be grown on them.