Aluminum-free strained-layer lasers emitting at 1.14 μm on low-composition InGaAs:n substrates by metalorganic chemical vapor deposition
Broad-area (W=150 /spl mu/m) single-quantum-well (SQW) lasers have been successfully fabricated on n-type In/sub 0.03/Ga/sub 0.97/As substrates without incorporating aluminum-containing alloys. The strained-layer InGaP-GaAs-InGaAs heterostructure was grown by atmospheric pressure metalorganic chemical vapor deposition. Due to both the increased substrate lattice constant and the partial strain compensation supplied by the tensile-strained GaAs optical guiding layers, a peak emission wavelength of 1.1403 /spl mu/m is obtained for a 1-mm cavity length.
In0.38Ga0.62As/InAlGaAs/InGaP Strained Double Quantum Well Lasers on In0.21Ga0.79As Ternary Substrate
An In0.21Ga0.79As ternary substrate has been fabricated using a newly developed multicomponent zone-growth method, and In0.38Ga0.62As/InAlGaAs/InGaP strained double quantum well lasers have been fabricated on the ternary substrate. Room temperature cw operation at a lasing wavelength longer than 1.2 µ m has been achieved on the ternary substrate for the first time. The lasers exhibited a low threshold current density of 280 A/cm2 and a characteristic temperature of 84 K, which were close to the designed values. It is also shown that the use of a wider band-gap barrier would enable a characteristic temperature higher than 150 K.
Hedy: A Gradual Language for Programming Education
One of the aspects of programming that learners often struggle with is the syntax of programming languages: remembering the right commands to use and combining those into a working program. Prior research demonstrated that students submit source code with syntax errors in 73% of cases and even the best students do so in 50% of cases. An analysis of 37 million compilations by 250.000 students found that the most common error was a syntax error, which occurred in almost 800.000 compilations. It was also found that Java and Perl are not easier to understand than a programming language with randomly generated keywords, stressing the difficulties that novices face in understanding syntax. This paper presents Hedy: a new way of teaching the syntax of a programming language to novices, inspired by educational methods by which punctuation is taught to children. Hedy starts as a simple programming language without any syntactic elements such as brackets, colons or indentation. The rules slowly and gradually change until the novices are programming in Python. Hedy is evaluated on 9714 programs.